A real-time database, an authentication system, storage and cloud functions. Plus other handy modules like notifications as you mentioned. In other words: a detached full backend. Firebase is an awesome product but it’s very expensive at scale and isn’t “migration” friendly.
Supabase is the FOSS alternative that you can fully self-host. They monetise it by providing cloud service for it. I’ve been following them for quite sometime and they are doing a great job.
At the center of everything is PostgreSQL which makes it highly scalable and easy to migrate if at some point you need to do it.
They are also big OS contributors to other popular repos like PostgREST which they rely on to provide the REST API. And as commented previously they have developed a native PG extension to give PG GraphQL capabilities.
They also integrate with flutter which could come handy at some point.
@George they are currently working on their CLI (available via homebrew and scoop) that could facilitate the integration as server model at some point. Plus the needed SC and AC components. I don’t know how many people use firebase model(I guess not many) but I think Supabase fits better Wappler’s philosophy.