PostgreSQL is the bigger, better brother of MySql. Less well-known, unfortunately.
Here are some links:
- http://www.postgresql.org/ - for it's home, and links to documentation etc.
- http://developer.apple.com/internet/opensource/postgres.html - on how to retrieve and compile PostgreSQL yourself. Also describes how to use it with Perl and PHP
- http://www.entropy.ch/software/macosx/postgresql/ - for a precompiled package one click install.