Realtime

Multiplayer / collaboration

• ★ Liveblocks — presence, comments, multiplayer cursors, Yjs/Automerge integration. Generous free tier; the easiest path to multiplayer.
• ★ PartyKit — Cloudflare-native; Durable Objects under the hood. Great for chat rooms, live cursors, custom multiplayer.
• Yjs — CRDT framework; pairs with WebSocket / WebRTC / IndexedDB providers. Used by Liveblocks, Tiptap collab, etc.
• Automerge — alternative CRDT; offline-first.
• TipTap + Hocuspocus — Tiptap's Yjs-backed collab server.

Pub/sub / messaging

• ★ Pusher Channels — battle-tested hosted WebSockets; free tier exists.
• ★ Ably — competitor; better realtime SLAs and presence APIs.
• Soketi — self-hostable Pusher protocol drop-in.
• Centrifugo — open-source realtime server; one of the best self-host options.

Bundled with platforms

• Supabase Realtime — Postgres CDC streamed to clients, plus broadcast/presence.
• Convex — every query is reactive by default.
• Firebase Realtime DB / Firestore — long-standing classic.

Lower-level

• socket.io — still huge in Node-only deployments.
• uWebSockets.js — fastest WebSocket lib for Node.
• Bun's native WebSockets — fast, ergonomic if you're on Bun.
• Cloudflare Durable Objects — single-instance stateful actors with WebSockets; the foundation for PartyKit and similar.

Sync engines (for offline-first apps)

See also Databases & ORMs:

• Replicache, Zero (Rocicorp) — sync engines.
• PowerSync, ElectricSQL — Postgres-backed sync.
• Triplit, InstantDB — full DB + sync layer.

Pick this if…

• Need cursors / comments fast: Liveblocks.
• All-Cloudflare: PartyKit.
• Self-host pub/sub: Centrifugo or Soketi.
• Already on Supabase / Convex: use the bundled realtime.
• Offline-first / local-first apps: Yjs + a sync engine, or Replicache/Zero.