I built SyncFlow to sync my Android SMS/MMS messages to my Mac and web — without relying on Google Messages or any third-party big tech cloud.

It runs on a dedicated server with a Node.js/Express API + PostgreSQL backend.

The Android app syncs messages, contacts, and call history, and you read/send them from a native Mac app or web client. Your messages never touch Google, Apple, or any third-party cloud.

Key technical decisions: - E2EE with Signal Protocol for message encryption - WebRTC for video/audio calls between devices - MMS attachments stored on Cloudflare R2 via presigned URLs - WebSocket for real-time message delivery + delivery status tracking - Firebase Auth for identity only — message data is fully separate

Stack: Kotlin (Android), Swift (Mac), Next.js (Web), Express + PostgreSQL (Server)

  What it does:
  - Read/send SMS and MMS from Mac or browser
  - Full contact and call history sync
  - Video and audio calling via WebRTC
  - File Transfer between your devices
  - Spam filtering and scheduled messages

Free tier: 200 messages/month. Paid removes limits.

  Downloads: https://sfweb.app/download

Would love feedback on the architecture especially the E2EE implementation and the MMS sync approach.