TouchDevelop is an on-device coding environment for hobbyists developed by Microsoft Research.
It allows pretty powerful scripts to be created, including full games.
The latest build, version 2.3, allows scripts to be pinned directly to your start screen with their own icons, and function very close to full-grown apps.
An example is Eddieâ€™s Send Contact script, which plugs a Windows Phone 7 hole by allowing users to send a People Hub contact via any of the build-in sharing mechanisms to some-one else.
If you feel like getting your hands dirty, you can find the increasingly powerful TouchDevelop app in Marketplace here.