I discussed the interactive Revit programming possibility offered by Daren Thomas' Revit Python shell a couple of times, originally for Revit 2010, then for Vasari, and for Revit 2012 and Vasari 2.1. It has been updated again since then, obviously, and is used a lot by the Vasari guys.
Now there is another interactive Revit programming environment available as well:
It sports the simplest installation I have ever seen for any Revit add-in whatsoever, the absolutely ultimate one-click RevitRubyShell installer, which sets up an external application creating its own simple single-button panel:
Clicking the button launches the Revit Ruby shell including a snippet of sample code that can be immediately executed by pressing the blue 'Run' arrow button:
Well worth looking at, and might prove a huge programming productivity booster.
Many thanks to Håkon for developing and sharing this!