Mosh

Mosh is a desktop-first, decentralized, end-to-end-encrypted messenger. The UI is Flutter; everything that must be right (OpenMLS, transport, storage, calls) lives in one Rust core, mosh-core, reached through flutter_rust_bridge. Peers find each other over the Moss mesh runtime; there is no central server.

Download

Windows installers and the macOS disk image are published on the Releases page, each with a SHA-256 checksum. The Windows installer is per-user (no admin prompt) and upgrades in place; message history is kept. The macOS DMG is a universal binary (Apple Silicon + Intel) — drag the app to Applications.

Mosh ships unsigned (see CODE_SIGNING.md); both platforms warn on first run.

• Windows — SmartScreen: More info, then Run anyway.
• macOS (12 Monterey or later) — Gatekeeper blocks the first launch: try to open the app once, then System Settings → Privacy & Security → Security → Open Anyway (the button appears for about an hour after the blocked attempt; enter your login password). This is Apple's documented flow. On macOS 14 and older the right-click → Open shortcut also works. The terminal equivalent is xattr -dr com.apple.quarantine /Applications/mosh.app.

Features

• Private 1:1 DMs — invite-URI onboarding with out-of-band fingerprint confirmation.
• Channels and private groups — multi-party conversations with their own membership and per-conversation DMs.
• Attachments and voice messages — chunked, encrypted file transfer with thumbnails, a media viewer and inline voice playback.
• Voice calls — encrypted real-time audio with jitter buffering.
• End-to-end encryption — OpenMLS group messaging over every channel.
• Decentralized discovery — Moss mesh-based peer discovery; users never enter hosts or ports in the primary flow.
• Encrypted persistent history — conversations and MLS session state survive restarts; the key is unlocked by user presence.
• English and Russian UI.

Architecture

• lib/ — the Flutter app. Features under lib/src/features/, Riverpod state under lib/src/state/, the generated bridge under lib/src/rust/.
• mosh-core/ — the Rust core: runtimes, adapters, crypto, the api/ facade the bridge exposes.
• moss/ — the Moss transport, a git submodule of redstone-md/moss built from Go into a shared library the core loads at runtime.
• docs/adr/ — the decisions, numbered.

Getting started

git clone --recursive https://github.com/redstone-md/mosh-flutter
cd mosh-flutter
node scripts/moss-prepare.mjs      # builds the Moss library (needs Go;
                                    # on macOS it is universal, arm64+x86_64)
flutter pub get
flutter run -d windows              # or: flutter run -d macos

Rust (see rust-toolchain.toml), Go and Flutter are required. AGENTS.md lists every build, test and packaging command.

Persistence and privacy

Message history and MLS state are encrypted at rest with a key held in the OS credential store. Uninstalling removes the app, not the history: a reinstall picks it back up. See ADR 0011 for the threat model.

Release notes

See CHANGELOG.md. Each GitHub release carries the changelog section for its version and the commits it contains.

License

See LICENSE.