I have been experimenting with SubText for a few weeks now, on a side project. So far, it has worked really well. SubText is written in C#, is open-source, and it is free.
There is a part of me that wonders if I should have used SubText rather than Community Server for Tod1d.net. I probably don't need 95% of the features that CS gives me, but, on the other hand, it is nice to know that they are there if I need them.