Syna

Syna is a LAN instant messaging app built with Kotlin Multiplatform + Compose Multiplatform. It runs on Android, Windows, and macOS with a fully peer-to-peer architecture — no central server, no internet required.

Features ✅ Multi-platform: Android (APK) + Desktop (Windows/macOS share the same JVM build) ✅ LAN peer discovery: UDP broadcast + multicast dual-channel, 3s heartbeat, 15s offline timeout ✅ Custom username: change it anytime in Settings, broadcast to LAN peers instantly ✅ WeChat-style chat: conversation list (unread badges / timestamps / previews), chat bubbles, ✓✓ read receipts, connection status display ✅ Connection mode switching: Auto / TCP (reliable) / UDP (fast) / Host Hotspot ✅ P2P mesh group chat: create → invite → mesh membership sync (JOIN/LEAVE), messages encrypted pairwise and delivered directly to each member — no central node ✅ Enhanced protection: End-to-end encryption: X25519 key exchange + HKDF-SHA256 + AES-256-GCM; private keys stay on your device only Burn after reading: message shows for 8 seconds, then is destroyed on both sides with BURN_ACK confirmation + 60s fallback Temporary chat: conversations auto-purge after a TTL (1h / 24h / 7d) on both devices ✅ Dark / light / system theme ✅ Offline messages: messages queue locally when the target is offline and are flushed automatically when they come back online ✅ Auto-reconnect: TCP heartbeat keep-alive + on-demand reconnection ✅ Private server (Minecraft-style): run your own headless chat server on Windows / macOS / Linux, join by IP:port + password from anywhere Persistent history on the server — late joiners pull the full backlog automatically Password-derived AES-GCM channel + password-derived group key encryption Burn-after-reading messages are purged from the server history too NAT traversal: just map the server port to the public internet with any tunnel tool (frp / ngrok / Tailscale) — the client only needs the public address:port