While not quite on topic, let me second that Firebird is a fine and under-appreciated RDBMS. Though it can obviously be used to run on your own server, it reall

While not quite on topic, let me second that Firebird is a fine and under-appreciated RDBMS. Though it can obviously be used to run on your own server, it really shines when it's deployed in the field. It's used for desktop software I help maintain, running at several hundreds of small businesses. The install is super lightweight, requires very little configuration and practically zero maintenance. Firebird strikes a nice balance when it comes to features. What's great is that it can be used with or without a server process. That way you can start using it like SQLite and scale up to a more PostgreSQL-like setup, or go the other way, with no effort. Many years later, we're still very satisfied with our choice at the time.