Hackety Hack is an interactive Ruby tutorial for the absolute beginner. It teaches the basics of programming from the ground up - no previous experience necessary. It's an open source desktop application and is available for Windows, OSX and Linux.
I like that it doesn't require a learner to flip back and forth between a tutorial and a text editor to learn and experiment with the code. Now we just need something like this for Assembly.
If you'd like to know more about the project, Hackety Hack
creator maintainer Steve Klabnik was recently interviewed on The Changelog.
In order to achieve cross-platform goodness, Hackety Hack was built on the cross-platform GUI toolkit Shoes.