These are things I’ve come across.
I haven’t actually used them.

JDiveLog is a Java-based open-source, so you can evolve it if you want to (provided you can write Java !).

There’s some software called Diving Log, which looks pretty comprehensive, and can output to .csv, UDCF or MySQL.
The data can be uploaded and shared using another piece called phpDivingLog.
And a WordPress plugin’s been written as well – you can find it here.
I think all of this is really cool.