Unturned is a free-to-play steam game that was featured by Alpha Beta Gamer a while back. Unturned is a zombie survival game in a semi-blocky style in that the world looks normal, while entities, items, and vehicles are made out of blocks. This game features multiplayer with a server hosting style similar to Minecraft. This game is a serious challenge, but also a ton of fun to play. The map is predetermined, but everything else is randomly generated. The game has driveable vehicles and also is populated with animals that can be killed and looted, along with, obviously, zombies that will try to kill you. This game is open world and has no real goal, meaning you can do whatever you want. This is possibly the best free survival game on steam, and you can get it here.
I was browsing IndieDB one day and a banner featuring Air Brawl came up. It looked cool, so I clicked it, and I'm glad I did. Air Brawl is a brand-new game whose development just started this spring. It's a plane-fighting game made on the Unity engine, and it is currently in pre-alpha development. The developer, Wilhem Nylund, has released a free-to-play demo on their IndieDB site, and the game looks promising. It's in third-person 3D view, and the game features 3 different planes to chose from with a variety of wacky weapons to equip on each, from homing missiles to a "Batapult." This game has online multiplayer that runs smoothly and is easy to connect to, making playing online very simple! (EDIT: I apologize for my earlier mistake of saying that this game was LAN only. The developer has informed me of my mistake.) This game is fast-paced,and it's a blast to play with friends, so this one is definitely worth a try! You can download the game here.