There is a proliferation of sync tools and little standardization. Here some in local-first space [0]. Martin Kleppmann in his talk last year spoke [1] the need for a generic sync protocol, which was very interesting.

[0] https://localfirstweb.dev/

[1] https://www.youtube.com/watch?v=NMq0vncHJvU&t=1016s

Someone maintains a list here

https://www.localfirst.fm/landscape

LiveStore shows recreating linear as one of their examples though I haven’t tried it. It was on the front page recently https://news.ycombinator.com/item?id=44105412

Firebase (Firestore is the DB) is the best I've ever used but not open source. MongoDB has Realm which achieves similar, is open source and is OK.

Realm's sync functionality (Atlas Device Sync) has been deprecated by MongoDB: https://www.mongodb.com/docs/atlas/app-services/sync/device-...