CRDT: Conflict-free replicated data type
Several interesting open source projects are working with CRDTs to make state synchronization in distributed systems an easier problem to deal with:  - Braid HTTP (https://braid.news/)
  - Automerge (https://github.com/automerge/automerge)
  - Gun (https://gun.eco/)
  - Yjs (http://y-js.org/)
  - Noms (https://github.com/attic-labs/noms)
  - DAT (https://dat.foundation/)

Personally, I'm most excited for Braid's effort to bring state sync to HTTP through the IETF process, as well as Automerge's progress in P2P via Hypermerge (and it's star app, Pushpin). I'd also like to see Gun succeed, but have had a hard time getting started due to visually distracting quirks in its documentation.