It puts three teams, Blufor, Opfor and Independents onto a map and let them fight over various randomly assigned objectives. For example, one might have an immobile helicopter that needs fuel. These are generally fought over pretty heavily as air transport is a huge boon. Others might be a tank that can be picked up from a location, or simply a pickup with a mounted gun or a weapon crate supply drop. You can also move various pieces of scenery by hand and by vehicle to assemble your own base. Also has a very basic currency system and various general stores and gun stores to buy supplies and equipment from. A few servers have even modified the game to have NPCs placed around objectives and having their own objectives around the map so you run into not only other players, but NPC groups as well.
It works out quite well if you can find people to work together with, but is quite painful if you can't. I was on the opfor team one night and a group of two people decided. "We're going to build our own base and none of you are allowed." So they teamkilled anyone that got near.
On the other hand, I was on opfor one night and found a group with a jackal(I believe a sort of british light recon vehicle) and we moved around assaulting various positions until all but me and one other guy left and then I flipped the jackal by accident and immediately afterward the other guy threw a grenade between us as we tried to get out without killing ourselves.
One more time, I forget the team, but we all were meeting up at zelenogorsk. Somehow the enemy found out about the meetup and managed to ambush us just as we were loading up to leave. Perfectly wrong time for us, as we were out of defensive positions and lining up to form a convoy. Several of us got sniped, I hid in some buildings and managed to kill a few before dying myself. Realized we were actually "outside" of the city and they had taken it. They had a respawn point in the city and the full advantage, so we had to spawn at another city and scavenge vehicles and weapons(usually didn't find those) and just rush back in unprepare. At the same time some allies managed to rush down to the unprotected enemy base and steal a few vehicles and a good number of weapons. We lost what we had in zelenogorsk, but gained quite a bit more.
Wasteland manages to give a very different experience than either vanilla arma2 or Dayz manages.
http://www.404games.co.uk/ - Homepage of the mission/mod.
There is a recently release mod that hopes to add persistence to equipment and bases, but if you want to try it out, it's just a mission for vanilla arma2 so all you have to do is filter out the wasteland servers in your vanilla arma2 server browser. 2.9b is the most recent version of the mission, but a lot of servers are still using 2.9 or 2.9a and a few are using even older versions or modified missions. As it is, don't get attached as everything you have will be lost when you log out and everything you build will be erased when the server resets(fairly often). Just play it for the experiences. Equipment comes pretty easily anyway, so even if you have to start over with just a makarov each time, you can still hope to find a vehicle in the first 5 minutes, and a decent set of equipment within 10-15. Not enough to take on the world on your own, but enough to join a group and contribute.