Ask HN: The state of Firebase alternatives in 2020?

Maybe not exactly what you're looking for but:

https://www.gun.eco/

Is open source Parse still going?

https://parseplatform.org/

There really isn’t a competitor. Supabase is trying to combine OSS tooling into a somewhat similar offering but it’s not nearly as feature rich as Firebase. That having been said, most people use Firebase for real time DB and auth, and Supabase supports that now. It doesn’t, however, support offline use cases, or any of the advanced functionality of firebase.

Pouch and couch solve the offline data scenario and live replication, but no auth story and the mapping of users to data is problematic (unless you build a proxy layer, there’s not an easy way to have some data be public, some private, and some shared).

Realm is paid these days, I believe, and it solves the data replication, but again, no auth.