I have a couple of open source projects, and a few more that have been in planning stage for a long time.
Highbase, a high availability cluster for MySQL was the most popular one (really, it’s somewhat popular). You might know it for it’s previous name, mysql-ha, too. It’s currently unmaintained, as it was made obsolete by newer projects such as mysql-mmm and flipper.
sh-mutex is a tiny but useful project that provides mutual exclusion locks in pure bash. Good if you’re a sysadmin. Some people have used it.
mydbsuggest was a set of tools for MySQL DBAs that aims to help them with database optimization (mostly table schema optimizations at this stage). I didn’t have enough knowledge of maatkit when I started this, which is a shame. The project is deprecated, once I switched to maatkit for my MySQL needs, I never looked back!