The Just Cause 2 Multiplayer Mod, which came out nearly two years ago, is getting a big update. The changelog is long, but the most significant additions are Steam achievements, scripting for NPCs, and an overhaul of the main menu.
On the achievements side, you've got examples like "Careful Down There", which you get for standing on top of a flying plane for one minute, or "Taxi Service" for... driving people around in a taxi. Example scripts include Wingsuit, Companions, and a minigame called 'Drift!'
If you want to try out the public beta of update 0.2, you can opt in via the Betas tab in JC2: Multiplayer's Steam properties menu.