railsday
The unofficial "RailsDay":http://www.43things.com/things/view/82899 was saturday, and a some interesting apps were made.
"All Consuming":http://new.allconsuming.net was remade in Rails by Erik Benson. It's an awful lot like 43Things, but for media you've read/watched/heard.
Next is the "search generator":http://www.43things.com/entries/view/43839 by Jeremy Hinegardner. It's not an application in itself, but a rails generator that adds generic indexing to your models. He "released v0.3":http://www.hinegardner.org/programming/ruby/SearchGenerator0.3.html today.
By the way, there needs to be a central rails authentication system set up. I've registered for so many little services, it's ridiculous. My latest is "Old News":http://oldnewsbaby.com.