I just launched Bling, a very lightweight alternative to Bundler. It's not as feature rich, but hasn't had nearly the hangups that Bundler has right now.
I put together an app called Love/HATE (open source) that lets developers love or hate something and send that up to a page. We have it on a TV here; it's hilarious (and informative).
I just put up a Rails OpenID engine that does almost all of the OpenID authentication work for you, minus a few simple steps, which you can read about here.
Locked Envelope is a service written in Ruby and Rails and allows users to send encrypted messages and attachments without any downloads. Backed by S3, running on Passenger.