What EldoS does

Callback Technologies, Inc. (operating as EldoS) is a privately held developer-tools company founded in 1998 and headquartered in Chapel Hill, North Carolina, with 11-50 employees. The company sells SDK components that bring kernel-mode filesystem and network driver capabilities to applications through clean user-mode APIs, eliminating the need for customer engineering teams to write, certify, and maintain their own kernel-mode drivers. Its product suite spans the CBFS line (Connect for virtual filesystems, Cloud for cloud-storage mounting, Filter for filesystem interception, Encrypt for transparent file encryption, Sync for bidirectional file synchronization, Vault for embedded encrypted containers, and Shell for Windows File Explorer extensions), plus the PCAP Filter for cross-platform network packet capture, and a family of standalone Callback Drive applications for S3, Azure, SFTP, WebDAV, and NFS.

The technical architecture pairs professionally developed, signed kernel-mode drivers (validated against Microsoft's filesystem test suites) with an event-driven user-mode API available in .NET, C++, Java, Python, Go, Rust, Delphi, Qt, macOS, JavaScript, Android, and iOS. Drivers handle low-level OS communication, signing, deployment packaging, and version management on behalf of customers. Over 25+ years the company has accumulated 4M+ deployments worldwide and 500+ enterprise customers including Box, three AWS product teams, Island Enterprise Browser, Boxcryptor (Secomba), Mountain Duck (Iterate), MyWorkDrive (a sister product built on CBFS Connect and deployed across thousands of organizations), Sony, BlackBerry, Adobe, Absolute Software, and CenturyLink.

Revenue is generated through a mix of perpetual and subscription SDK licensing, tiered annual support and maintenance contracts, and subscriptions for the standalone Callback Drive applications. Go-to-market combines a product-led-growth model (free 30-day fully functional trial with direct download and free technical support during evaluation) with an enterprise sales motion for production deployments requiring quote-based pricing, dedicated engineering access, and guaranteed response SLAs. The company is bootstrapped, with no disclosed funding rounds, no parent entity, and no subsidiaries, and operates as a horizontal developer-tools vendor serving software engineering teams, enterprise technology companies, and cloud storage providers.

Name

EldoS

Legal name

Callback Technologies, Inc.

Website

https://eldos.com

Company type

Private

Founded year

1998

Operating status

Operating

Headcount range

11–50 employees

Short description

Callback Technologies (EldoS) is a Chapel Hill, NC-based developer-tools company founded in 1998 that sells SDK components for virtual filesystems, file filtering, transparent encryption, file sync, and cloud storage mounting, enabling software teams to add kernel-level filesystem and network capabilities without writing kernel driver code.

Ownership category

akta.pro rank

Product category

Developer SDK Components for Filesystem and Storage Infrastructure

NAICS

Computer Systems Design and Related Services (5415), Computer Systems Design and Related Services (54151)

SIC

Services-Computer Programming Services (7371), Services-Computer Programming, Data Processing, Etc. (7370)

akta.pro primary industry

Developer Tooling & SDK Platforms (BPAMAOAD)

Keywords

• Filesystem driver components
• Virtual filesystem SDK
• Cloud storage mounting
• Transparent file encryption
• Network packet capture

Headquarters

HQ city

Chapel Hill

HQ country

United States

HQ region

North America

Markets served

GTM type

B2B

Offering type

Software

Cost components

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

Revenue model

1. SDK/License Sales: Perpetual and subscription licensing for CBFS SDK components. CBFS Developer Subscription available for teams needing multiple components.
2. Annual Support and Maintenance: Tiered professional support for production deployments including guaranteed response times and dedicated engineering access for enterprise teams.
3. Callback Drive Applications: Ready-made standalone applications for mounting remote or encrypted storage as local drives. No development required.

Pricing tiers

Go-to-market motion3 records

Distribution channels4 records

Marketing channels5 records

Core offering

Callback Technologies (operating under the EldoS brand) develops and licenses a suite of SDK components that enable software developers to add virtual filesystems, filesystem filtering, transparent file encryption, file synchronization, cloud storage mounting, and network packet capture capabilities to their applications without writing kernel-mode driver code. The company pairs professionally developed and signed kernel-mode drivers with clean user-mode APIs available across .NET, C++, Java, Python, Go, Rust, Delphi, Qt, and JavaScript. It also ships standalone Callback Drive consumer/SMB applications that mount S3, Azure, SFTP, WebDAV, and NFS storage as local drives.

Product overview

Callback Technologies offers a suite of SDK components for adding system-level filesystem capabilities to applications without writing kernel-mode driver code. The core CBFS product line includes: CBFS Connect (virtual filesystems), CBFS Cloud (cloud storage mounting), CBFS Filter (filesystem filtering/monitoring), CBFS Encrypt (transparent file encryption), CBFS Sync (file synchronization), CBFS Vault (encrypted file containers), CBFS Shell (Windows Explorer extensions), and PCAP Filter (network packet capture). Additionally, the company offers standalone Callback Drive applications for Amazon S3, Microsoft Azure, SFTP, WebDAV, and NFS. The architecture pairs professionally developed kernel-mode drivers with clean user-mode APIs available in .NET, C++, Java, Python, Go, Rust, Delphi, and Qt. CBFS Connect, CBFS Sync, CBFS Vault, and PCAP Filter support Windows, Linux, and macOS; CBFS Filter and CBFS Encrypt are Windows-only due to minifilter driver architecture; CBFS Vault also supports Android and iOS.

Differentiator

Problem solved

Functional benefit

Brands

• Callback Drive: Standalone applications that mount remote or encrypted storage as local drives without development required. Includes Callback Drive for SFTP Servers, Amazon S3, Microsoft Azure, WebDAV Servers, and NFS Servers.
• CBFS Developer Subscription
• MyWorkDrive

Products and services

• CBFS Connect
• CBFS Cloud Cloud storage mounting SDK that programmatically mounts cloud and remote storage (S3, Azure Blob, Azure Files, OneDrive, SharePoint, Google Drive, WebDAV, SFTP, NFS) as local virtual drives with a single Mount() API call, including local read/write cache, background sync, and conflict detection.
• CBFS Filter
• CBFS Encrypt Transparent file encryption SDK that enforces file-level encryption policies; authorized processes decrypt on the fly while all other processes see ciphertext. Windows-only.
• CBFS Sync
• CBFS Vault Encrypted storage SDK that embeds a complete encrypted filesystem inside a single portable file, featuring per-file and whole-vault encryption, compression, journaling, and random read/write access.
• CBFS Shell Windows shell extension SDK that customizes File Explorer with virtual folders, context menus, overlay icons, and detail columns without risking Explorer stability.
• PCAP Filter Network packet capture and filtering SDK that captures, filters, and modifies network packets in real time using BPF filter syntax compatible with libpcap and Wireshark. Cross-platform support for Windows, Linux, and macOS.
• Callback Drive for Amazon S3
• Callback Drive for Microsoft Azure Standalone application that connects to Microsoft Azure storage and enables working with files directly from File Explorer without Azure-specific tooling.
• Callback Drive for SFTP Servers Standalone application that enables accessing files over SFTP through standard Windows file APIs without mapping a network share or managing a separate client.
• Callback Drive for WebDAV Servers Standalone application that provides access to WebDAV-hosted files as if 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.
• CBFS Developer Subscription

Quantifiable outcome

• 4M+ deployments worldwide
• +3 more outcomes

Named customers10 records

Segments3 records

Ideal customer profiles2 records

Technology focussed Yes

API detail

Has API

Yes

API docs

API detail

Core technology

AI maturity

App detail

Integration8 records

Feature10 records

Scale indicators4 records

Recent moves5 records

Expansion highlights5 records

Direct peers

• Iterate (Mountain Duck): Builds Mountain Duck and Cyberduck for mounting cloud and remote storage (S3, SFTP, WebDAV, Azure) as local drives. Also an EldoS customer using CBFS Cloud, but operates comparable standalone products in the same category.
• MSP360 (CloudBerry Lab): Provides cloud storage management, backup, and drive-mounting tools for S3, Azure, and other backends. Overlaps with Callback Drive applications and CBFS Cloud in cloud-to-local drive integration scenarios.
• GoodSync: File synchronization and backup software with bidirectional sync across local drives, servers, and cloud storage. Directly comparable to CBFS Sync's functionality in cross-platform file synchronization.
• WinFsp (Dokan): Open-source FUSE-compatible filesystem layer for Windows. EldoS explicitly compares CBFS Connect to FUSE and Dokan, making this the most direct open-source substitute for the company's flagship virtual filesystem SDK.
• NetLib: Provides Encryptionizer for file, folder, and disk encryption at the kernel level. Competes directly with CBFS Encrypt in the transparent file encryption and access-control category.
• ExpanDrive: Maps cloud storage (S3, Google Drive, Dropbox, OneDrive, SFTP, WebDAV) as local drives on Windows, macOS, and Linux. Directly competes with Callback Drive applications and the CBFS Cloud use case for cloud storage mounting.

Broad incumbents

• Dropbox (Boxcryptor): Acquired Boxcryptor, which was both an EldoS customer and a transparent file encryption product competing in the same encryption-for-cloud-storage category as CBFS Encrypt. Dropbox now bundles this capability into a much broader file-sync platform.
• Wireshark / libpcap: Open-source reference for network packet capture with the libpcap filter syntax that PCAP Filter is explicitly compatible with. EldoS positions PCAP Filter as a cross-platform, production-grade SDK wrapper around the same filter semantics.
• Microsoft (Windows Minifilter / IFS / Project Reunion): Provides the underlying Windows minifilter and Installable File System (IFS) platforms on which CBFS Filter and CBFS Encrypt are built, and ships first-party equivalents for many filesystem and shell-extension capabilities via Windows APIs and PowerToys.

Emerging players

• Pismo: File management and conversion platform serving developers and enterprises. Adjacent to EldoS's developer-tooling focus with overlap in file processing APIs, though Pismo emphasizes cloud-native application platforms rather than kernel-mode filesystem components.

Market position

Strengths5 records

Weaknesses5 records

Competitive moat5 records

Key risks6 records

Key highlights7 records

Customer concentration

• Xx.com/eldoscorp
• Facebookfacebook.com/EldoSCorporation
• LinkedInlinkedin.com/company/eldos-corporation

Revenue estimate

Valuation estimate

Number of profiles

Funding overview

Funding rounds

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 EldoS