Jeweled detritus

Ruby on Rails is a popular web development kit, which uses the object-oriented scripting language, Ruby, and the web development framework known as MVC.
I think a handful of site (including Twitter) were built with RoR, and it's amazing how quickly you can implement some pretty powerful stuff.
If you're looking to get started with RoR, I found this wonderful list of 12 RoR Tutorials.