PocketBase is an open source Go backend that has embedded realtime database, files and users management, admin UI and REST-ish API, all compiled in 1 portable file. Think of it as a lightweight alternative to Firebase or Supabase.
Looking beyond PocketBase? Try Supabase for Postgres, auth, and edge functions; Appwrite for a developer-friendly cloud and broad SDKs; Convex for a reactive data model and functions; Altogic for visual workflows; or Parse Server for a self-hosted Node backend.