Achieve That! is a mod for Skyrim that, as you've probably picked up from the headline, adds 109 new achievements to the game, in case you've racked up all the existing ones already.
What's neat here is that they're actually really cool; way cooler than Skyrim's fairly boring official ones. Most of them reward you for doing the things that the game does best: exploring, cataloguing, doing everything the game is offering to let you do.
So there's an achievement for finding 13 pilgrim stones.
The best part, though, is your reward. Instead of just ticking a box or giving you points, you're rewarded with in-game perks. Open 150 chests, for example, and you earn +10 for your carrying weight. Read 100 books and get +2 speechcraft.