Grasshopper for Rhino has been recently released for Rhino after being earlier released as Explicit History.
http://en.wiki.mcneel.com/default.aspx/McNeel/ExplicitHistoryPluginMainPage.html
I have been playing with Grasshopper a lot. It is really a fun plugin. It basically give users parametric capabilities (generating linked components) without having to learn very much. Plus the visual aspect of it is very nice.
If you have Rhino give it a try.
There are some good tutorials at:
http://www.designreform.net