Any other databases on single disk file like SQLite exist?
What are other databases like SQlite, which dont require spinning up a server & save data to disk instead? Does such a thing exist for specialized databases on a single disk (elastic search etc)?
There's duckdb which seems very similar. I haven't actually used it for anything yet so YMMV.
Apache H2, and Apache Derby. There's quite a few that are available if you only need them to be supported on the JVM.
What are your requirements (data model, non-functional priorities, data size, data types)?