Secure self-hosted team chat platform Chatto goes open source

German developer Hendrik Mans has released the source code for Chatto, a privacy-focused team messaging platform, making the project open source and available for anyone to self-host.

The milestone fulfills a promise made when the project was first unveiled in late 2025 and opens the software to public scrutiny for the first time.

The project is licensed under AGPL-3.0-or-later, with Apache-2.0 exceptions covering components such as the standalone frontend, documentation, examples, and integration surfaces. Installation packages are available for Linux, macOS, and Windows.

Mans first introduced Chatto in December 2025 as an alternative to commercial workplace collaboration platforms such as Slack, Microsoft Teams, and Discord. Designed to simplify self-hosting while maintaining a familiar user experience, the project aims to eliminate the complex infrastructure that self-hosted messaging platforms often require.

Chatto is a group chat application designed around a single-community server model. Each server hosts one organization or community, with no federation between independent instances. Users who participate in multiple communities simply connect directly to multiple servers. The application is designed to run as a standalone binary without requiring external databases, message brokers, or cache servers, while also serving its own web frontend.

Version 0.4 adds functionality that was still on the roadmap when the project was announced, including built-in voice and video calls with screen sharing. According to Mans, calls are end-to-end encrypted, while stored personal information and chat data are encrypted at rest using per-user encryption keys that are destroyed when a user deletes their account. The platform also exposes client and server extension APIs for building custom clients, bots, and integrations.

Although Chatto places a strong emphasis on privacy and security, its claims have not yet been independently validated through a publicly disclosed third-party security audit. Making the source code available enables researchers and developers to inspect the implementation, evaluate its cryptography and security architecture, and identify potential vulnerabilities, but that review process will take time. Until then, users should treat the project's security guarantees as developer claims rather than independently verified assurances.

The software also remains in an early stage of development. Chatto is currently at version 0.4.2, which Mans considers suitable for production deployments, but additional moderation capabilities, client improvements, and other features are planned before a 1.0 release expected within the next six to twelve months. The developer also notes that breaking changes may still occur as development continues, making regular updates important for self-hosted deployments.

While the code is now publicly available, the project is not currently accepting outside code contributions. Development will be led solely by Mans at this stage.

Alongside the open-source release, Mans also announced Chatto Cloud, a managed hosting service that will soon enter public beta. The hosted offering will provide managed Chatto servers on European-owned infrastructure with automatic scaling, nightly backups, and zero-downtime upgrades. Organizations will be able to migrate between Chatto Cloud and self-hosted deployments without proprietary lock-in.