Easy achievements has just been submitted to the Unity Asset Store. It should be available soon.
Easy achievements is an extension to the unity editor that allows for rapid creation and easy use of achievements within your existing application.
For more information see this page.
A question came up in the #unity irc channel on freenode.net, about how the world was done in Animal Crossing. I made a small demo that uses a custom shader to get a similar effect.
Here is a simple demo of the effect: WebPlayer (move with the w/s keys)
And here is the unitypackage containing the shader and a sample scene: UnityPackage