I still remember interbase, now called firebird. Of course, sqlite is much more prominent today for an embeded database, but for the times without sqlite...
It has all the downsides of service based DB without all the advantages of file based DB.
And the documentation is way below average, backwards compatibility is a joke.
Not to mention the 3rd party software had to design their own(horribly bad) way to handle geometry in firebird... and they keep transactions open forever - and bloody firebird prior to 2.5 had no way to drop the dead connections.