I'm porting Chimailmadmin, an email management tool I've been working on for a couple of years, to Sinatra.
Actually I'm working on porting a bunch of web applications I work on, but Chimailmadmin is the furthest along.
I'm glad I held off for a bit while I became more familiar with Sinatra. Its a really sweet little web application framework.
And yes - its open source (Affero GPLv3) and available on Github!