What Callback Technologies does

Callback Technologies, Inc. is a privately held, Chapel Hill, North Carolina-based software company founded in the late 1990s that develops and sells developer SDK components for filesystem, storage, encryption, and network operations on Windows, macOS, Linux, iOS, and Android. The company's core technology pairs professionally developed, signed, kernel-mode filesystem and network drivers with clean user-mode callback APIs available in .NET, C++, Java, Python, Go, Rust, Delphi, Qt, JavaScript, and Swift, enabling developers to ship low-level OS features without writing or maintaining kernel driver code. Its product portfolio includes CBFS Connect (virtual filesystems), CBFS Filter (filesystem/registry/process interception via minifilter driver), CBFS Cloud (cloud storage mounting for 10+ backends), CBFS Encrypt (transparent file encryption with process-based access control), CBFS Sync (cross-platform file synchronization using native OS sync APIs), CBFS Vault (encrypted filesystem-in-a-file containers), CBFS Shell (Windows Explorer extensions), PCAP Filter (cross-platform packet capture/filtering), CBFS Disk (virtual block-level disk drives), and a set of ready-made Callback Drive applications for S3, Azure, SFTP, WebDAV, and NFS.

Callback Technologies operates a product-led growth motion supported by content marketing: customers can download a fully functional 30-day trial with no feature restrictions, evaluate via comprehensive documentation and knowledge base content, and either self-purchase online or engage direct sales for enterprise/OEM agreements. Revenue is generated primarily through perpetual per-developer-seat SDK licenses with optional annual maintenance/subscription for upgrades and support, supplemented by OEM/royalty licensing for ISVs embedding components in distributed products, a Value-Added Resellers channel, standalone Callback Drive application licenses ($99 desktop, $499 server for S3 Drive), and paid premium support tiers. The company reports 4M+ deployments worldwide and 500+ enterprise customers, including Sony, Box, three AWS product teams, Island Enterprise Browser, Boxcryptor, Mountain Duck, and MyWorkDrive, the last of which is built entirely on CBFS Connect and deployed across thousands of organizations.

The business targets a horizontal developer and security-software-vendor audience, with primary use cases spanning virtual drives, cloud sync clients, encrypted file containers, endpoint security and DLP agents, network monitoring tools, and DRM/records management. Callback maintains technology partnerships with AWS, Microsoft, and Apple at the platform level, and is in compliance with GDPR, PCI DSS (via payment processor), and Section 508. As of mid-2024, the company has 11–50 employees, recently raised a $2.5M funding round, and has hired a CFO, indicating a transition toward more formalized financial and growth operations while remaining founder-controlled and privately held.

Name

Callback Technologies

Legal name

Callback Technologies, Inc.

Website

https://callback.com

Company type

Private

Founded year

1998

Operating status

Operating

Headcount range

11–50 employees

Short description

Callback Technologies develops and sells cross-platform developer SDKs — including CBFS Connect, Filter, Cloud, Encrypt, Sync, Vault, Shell, and PCAP Filter — that expose kernel-mode filesystem, encryption, and network capabilities through user-mode APIs, serving software developers, security vendors, and ISVs across more than 500 enterprise customers.

Ownership category

akta.pro rank

Product category

Filesystem Development SDKs

NAICS

Computer Systems Design and Related Services (5415)

SIC

Services-Prepackaged Software (7372), Services-Computer Programming Services (7371)

akta.pro primary industry

Developer Tooling & SDK Platforms (BPAMAOAD)

akta.pro secondary industries

Data/Apps Connectivity & Adapters (Connectors, Drivers, SDKs) (HDAEAIAK), Developer Portals, SDKs & Documentation Platforms (BPAMADAG)

Keywords

• Virtual filesystem SDK
• Filesystem filter drivers
• Cloud storage mounting
• File encryption SDK
• Kernel driver development

Headquarters

HQ city

Chapel Hill

HQ country

United States

HQ region

North America

Offices1 record

Markets served

GTM type

B2B

Offering type

Software

Cost components

Technology or R&D, Personnel, Operations, Marketing or Sales, Infrastructure

Revenue model

1. Developer SDK Licenses: Per-seat developer licenses for SDK products (CBFS Connect, Filter, Sync, Shell, Vault, Encrypt, PCAP Filter). Each license permits one developer to build any number of applications using the SDK and deploy royalty-free to unlimited end-user machines. Licenses are perpetual for the purchased version.
2. Annual Maintenance/Subscription: Optional annual maintenance subscriptions covering major version upgrades and extended support entitlement beyond initial coverage period. Subscription terms are 12 months and renew automatically unless terminated.
3. Callback Drive Applications: Ready-made applications for mounting remote storage as local drives. Desktop licenses and Server licenses available. Server licenses include unlimited users and priority support.
4. Volume and OEM Licensing: Volume discounts for teams purchasing multiple developer seats. OEM pricing for ISVs embedding components in products distributed to their own customers, typically including custom royalty structures, extended support terms, and source code escrow options.
5. Premium Support Add-on: Priority support tier available as paid add-on at purchase or anytime afterward. Provides guaranteed response within one business day, direct access to engineers, debugging support, and sample application creation.
6. Custom Development Services: Professional services for building specific features, custom integrations, or specialized implementations not addressed by the standard SDK.

Pricing tiers

Go-to-market motion1 record

Distribution channels3 records

Marketing channels5 records

Core offering

Callback Technologies develops and sells a suite of developer SDK components for building virtual filesystems, filesystem filtering, transparent encryption, file synchronization, and cloud storage integration into applications. The SDKs pair pre-built, signed kernel-mode drivers with clean user-mode callback APIs available across 13+ programming languages, enabling developers to add system-level filesystem capabilities without writing kernel driver code. The company also offers ready-made Callback Drive applications that mount remote and cloud storage as local drives without development.

Product overview

Callback Technologies offers a suite of developer SDK components for filesystem and network operations without requiring kernel driver development. The product portfolio consists of two main categories: (1) Developer Components - CBFS Connect (virtual filesystems), CBFS Filter (filesystem filtering), CBFS Cloud (cloud storage mounting), CBFS Encrypt (file encryption), CBFS Sync (file synchronization), CBFS Vault (encrypted containers), CBFS Shell (Windows Shell extensions), PCAP Filter (packet capture), and CBFS Disk (virtual disk drives); and (2) Virtual Drive Applications - ready-made standalone applications (Callback Drive) for S3, Azure, SFTP, WebDAV, and NFS. All products provide pre-built signed kernel drivers paired with clean user-mode APIs available in .NET, C++, Java, Python, Rust, Go, Delphi, Qt, and JavaScript.

Differentiator

Problem solved

Functional benefit

Brands

• CBFS Connect: SDK for creating and managing virtual filesystems from almost any type of storage.
• CBFS Filter
• CBFS Cloud
• CBFS Encrypt
• CBFS Sync
• CBFS Vault
• CBFS Shell
• PCAP Filter
• Callback Drive

Products and services

• CBFS Connect Cross-platform SDK for creating and managing virtual filesystems from almost any type of storage. Allows developers to present any data source (cloud storage, databases, REST APIs, or custom content) as a fully functional drive with folders and files visible to the OS and all applications via standard file APIs. Supports NTFS-level features including named streams, hard links, reparse points, file locking, quotas, and NTFS security (ACL) mechanisms. Includes a FUSE-compatible API.
• CBFS Filter Windows SDK that allows applications to intercept, monitor, and control filesystem, Windows Registry, and process and thread operations in real time using a pre-built minifilter driver with callback-based user-mode API. Enables antivirus, DLP, access control, and audit logging applications without writing kernel driver code. Includes CBRegistry for registry control, CBProcess for process monitoring, and CBMonitor for passive filesystem monitoring.
• CBFS Cloud SDK for programmatically mounting cloud and remote storage as local virtual drives. Supports S3-compatible, Azure Blob, Azure Files, OneDrive, SharePoint, Google Drive, WebDAV, SFTP, and NFS connection types. Single API with consistent behavior across all backends. Includes local read/write cache with background sync and conflict detection.
• CBFS Encrypt Windows SDK for enforcing transparent file encryption policies with process-based access control. Uses a minifilter driver to automatically encrypt files on disk and decrypt on the fly for authorized processes. Rules-based engine targets specific directories, file extensions, or filename patterns. Modern cryptographic algorithms for security and performance.
• CBFS Sync Cross-platform SDK for building bidirectional file synchronization between local filesystems and cloud storage. Uses OS-level sync infrastructure: Cloud Filter API on Windows, File Provider on macOS, FUSE on Linux. Displays native OS sync status icons. Supports placeholder files and on-demand hydration.
• CBFS Vault Cross-platform SDK for creating and managing self-contained file storage containers (a filesystem within a file). Supports per-file and whole-vault encryption, compression, journaling for crash resilience, random read/write access, alternate data streams, and custom metadata. Runs on Windows, Linux, macOS, Android, and iOS.
• CBFS Shell Windows SDK for extending and customizing Windows File Explorer with virtual folders, custom context menus, overlay icons, custom detail columns, and more using an out-of-process architecture for stability. Supports managed .NET code (not possible with traditional in-process COM-based extensions).
• PCAP Filter Cross-platform driver and component library for real-time network packet capture and filtering. Uses BPF filter syntax compatible with libpcap and Wireshark. Adds real-time packet modification, drop capabilities, and consistent API across Windows, Linux, and macOS.
• CBFS Disk Library for creating and managing virtual block-level disk drives that the OS sees as raw storage devices. Standard filesystems like NTFS or FAT are formatted on top of the virtual disk by the OS. Windows-only.
• Callback Drive for Amazon S3 Standalone application that mounts S3-compatible storage as a local drive. Browse, open, and edit files stored in S3 directly from File Explorer without sync or local copy. No development required.
• Callback Drive for Microsoft Azure Standalone application that mounts Azure storage as a local virtual drive. Browse and interact directly with remote files like they are on the local machine. Supports Azure Blob and Azure Files services.
• Callback Drive for SFTP Servers Standalone application that mounts SFTP servers as local drives. Supports Windows, Linux, and macOS with password, public key, keyboard-interactive, multi-factor, and physical security key (PKCS11/YubiKey) authentication.
• Callback Drive for WebDAV Servers Standalone application that mounts WebDAV-hosted files as if they were stored locally. Compatible with any server that speaks the WebDAV protocol.
• Callback Drive for NFS Servers Standalone application that accesses files hosted on NFS servers directly from File Explorer using standard Windows file APIs without additional client software.

Quantifiable outcome

• No kernel driver code required - developers write application logic while Callback maintains the infrastructure layer
• +1 more outcomes

Named customers7 records

Segments4 records

Ideal customer profiles4 records

Technology focussed Yes

API detail

Has API

No

API docs

API detail

Core technology

AI maturity

App detail

Integration11 records

Feature9 records

Partnerships

Three partnerships are on record, tiered core.

• Amazon Web ServicescoreTechnology or IntegrationAWS is both a customer and platform partner. Three AWS product teams depend on Callback Technologies components for filesystem and network infrastructure. CBFS Cloud supports S3-compatible storage as one of its 10+ connection types. Callback Drive for Amazon S3 provides direct integration with S3 storage.
• MicrosoftcoreTechnology or IntegrationCallback Technologies products are deeply integrated with Microsoft platforms: CBFS Filter uses Windows minifilter driver architecture, CBFS Sync uses Cloud Filter API, products support Azure storage, OneDrive, and SharePoint. Products are validated against Microsoft's own filesystem test suites.
• ApplecoreTechnology or IntegrationCallback Technologies products support macOS, iOS, and Swift platforms. CBFS Sync uses File Provider API on macOS. Products handle Apple's restrictions on kernel extensions with alternative approaches (NFS component for driver-free operation on macOS).

Scale indicators3 records

Recent moves6 records

Expansion highlights6 records

Direct peers

• South River Technologies: South River Technologies builds commercial filesystem, SFTP/FTP server, and MFT components (Titan FTP Server, WebDrive, Cornerstone MFT) that developers and ISVs embed — directly comparable to Callback Technologies' combination of kernel-level SDKs plus ready-made file-server applications.
• /n Software: /n Software sells developer component libraries (IPWorks, CloudStorage toolkit, File System toolkit, SFTP/SSH components) with per-developer licensing models nearly identical to Callback's CBFS line; both sell cross-platform SDKs to ISVs building file, storage, and network features.
• Eldos Systems: Eldos has historically offered very similar kernel-mode filesystem drivers and components (SolFS, RawDisk, CBFS-Variant-class products) to Callback Technologies; it competes in the same niche of commercial virtual filesystems and encrypted containers for developers.
• WEOnlyDo: WEOnlyDo sells commercial SSH, SFTP, and WebDAV developer components for Windows — overlapping directly with Callback's SFTP/WebDAV mounting and authentication capabilities and competing in the same per-developer SDK channel.
• Chilkat Software: Chilkat provides cross-platform developer libraries for SFTP, SSH, encryption, file compression, and cloud storage (S3/Azure) — overlapping with the encryption, SFTP, and cloud-mounting portions of the CBFS portfolio under a similar per-developer licensing model.

Emerging players

• Cryptomator: Cryptomator builds transparent client-side encryption for cloud storage drives using virtual filesystems (FUSE on macOS/Linux, WinFsp on Windows) — comparable architecture to CBFS Vault/Encrypt, with overlap in the secure-file-container use case but positioned as low-cost/open-source rather than commercial SDK.
• WinFsp (Windows File System Proxy): WinFsp is a user-mode filesystem framework used by projects like Cryptomator and rclone to mount remote/cloud storage on Windows — overlapping with CBFS Connect/Cloud as an alternative commercial or open-source route to the same virtual-filesystem outcome.
• Dokan (Dokany): Dokan/Dokany provides a user-mode filesystem framework widely used in cloud-sync and encryption tools on Windows; it overlaps with CBFS Connect's FUSE-compatible API positioning as a community-driven alternative to Callback's commercial drivers.

Broad incumbents

• Microsoft (Azure / Windows Storage SDKs): Microsoft supplies the Cloud Files API and Azure Storage SDKs that CBFS Sync/Cloud integrate with, and ships Windows minifilter infrastructure Callback builds on — as a broad incumbent it could shift APIs in ways that affect Callback, but also as the platform vendor that defines the surface Callback must support.
• OpenText (HPE/HPI OpenText file components): OpenText's portfolio (which absorbed several legacy developer-component and MFT lines, formerly from Sterling Commerce and a number of smaller SDK vendors) competes broadly with Callback in secure file transfer, encrypted storage, and enterprise file access for large regulated customers.

Market position

Strengths5 records

Weaknesses5 records

Competitive moat4 records

Key risks6 records

Key highlights7 records

Customer concentration

• LinkedInlinkedin.com/company/callback-technologies-inc

Compliance3 records

Revenue estimate

Valuation estimate

Number of profiles

Profiles1 record

Funding overview

Funding rounds1 record

Investors

Funding detail is available on the Subscription and Enterprise plan.Contact sales →

M&A

Investments

M&A and investment is available on the Subscription and Enterprise plan.Contact sales →

Frequently asked questions about Callback Technologies