Sqlite on an embedded system
The smallest sqlite3 I came up with was 327 KBytes (for PowerPC), which was sufficient for the system so I stopped trying to make it smaller. This was the full sqlite3 CLI binary, the C APIs alone would have been somewhat smaller.
I had set SQLITE_OMIT_AUTHORIZATION, SQLITE_OMIT_EXPLAIN, SQLITE_OMIT_PROGRESS_CALLBACK, and SQLITE_OMIT_TCL_VARIABLE to trim the size of the binary, and used -Os to get it to that size.
If you don't need the full power of SQL it might be interesting to look into alternative solutions, like Berkeley DB.