Progress is an achievement framework for Unity3D released under the MIT license. If you want something similar to Xbox achievements or PlayStation trophies in your Unity3D game, then Progress is likely a decent place to start.
This is a small project that I threw together quickly because I didn't have time to do the full 7 Day Roguelike Challenge, so the code quality isn't the best and sadly there's no test coverage - maybe in the future I'll find the time to improve the project. I do know of at least one shipping product that used this framework, so there's some interest.
Last tested with Unity 4.3.2f1.
View a simple example in the Unity Webplayer here.
For more information you can check out my blog post here, which includes a rundown of how to setup some basic achievements.