This is a video demo of Addon Studio for Visual Studio - the demo shows how they've enabled the creation of World of Warcraft mods using Visual Studio. It looks incredibly easy to use, and could open up plenty of non WoW based modding opportunities.
On a side note, this is probably the only time a single topic post is going to have this combination of tags!
Link: Curse: AddOn Studio Demonstration
Link: Codeplex: AddOn Studio for World of Warcraft