Co-Op

Blast your way through historic Mars with a crack team of up to 4 friends. Marvel and rejoice at vast expanses of lovingly handcrafted pixels. Brave the hostile Martian frontier armed with 1619’s finest steam-punk weaponry. Master innovative co-op mechanics paired with classical top-down shooter gameplay. Climb the online leaderboards in single-player classic arcade mode.

Bunch of Heroes is a humorous 4 player cooperative top-down shooter for Windows through Steam. The game has online co-op with up to 4 players.

The Bunch, is the most formidable team of fighters from different parts of the world ever assembled. In the game the Earth is under attack, An Alien Invasion is threatening all of humankind, with no regard to gender, color or nationality. And these nasty Aliens have a powerful Zombie Army.

Age of Empires Online (abbreviated AoEO), is a history-based RTS. The game is free-to-play—it is free for users to play, with the additional option of earning or purchasing premium content. Premium content may include access to many special items and blueprints, and more quests and features. Also, booster packs are now available, such as Defense of Crete and Skirmish. This former gives the player the ability to play in a survival type mode game, while the latter allows up to four humans versus up to four CPU opponents in a more traditional skirmish gamemode. (Soure: Wikipedia)

Alien Breed 2: Assault, like Evolution, is an isometric shooter set on board a futuristic spacecraft. In each level, the main character Conrad is given a series of tasks such as collecting key cards, restoring power, or escorting innocents, which he must complete before finding that level's exit. Standing in his way are a variety of aliens who will attack him, usually en masse. He can also suffer damage from explosions, fires, electrical disturbances, and enemy turrets. Conrad can run and shoot in all directions, and can collect a number of different weapons and items to aid him.

Darkest Hour: Europe '44-'45 is an independently developed Western Front modification for Tripwire Interactive's acclaimed first-person shooter, Red Orchestra: Ostfront 41-45.

Darkest Hour focuses on the Allied invasion from the Normandy campaign in 1944, through the failed Operation Market Garden in Holland and beyond the Battle of the Bulge. It covers not only the intense infantry battles the campaign is so well known for, but also includes the epic large scale tank battles that took place in the later stages of the war.

Counter-Strike: Global Offensive (CS:GO) expands upon the team-based action gameplay that it pioneered when it was launched 12 years prior.

CS:GO features new maps, characters, and weapons and delivers updated versions of the classic CS content (de_dust, etc.). In addition, CS:GO introduces new gameplay modes, matchmaking, leaderboards, and more.

Diablo III is the long awaited installment in the Diablo series from Blizzard. The gameplay is a genre-defining "action RPG" that is known for it's one click per attack, and extensive "loot" system which offers near limitless upgrades to weapons, items and armor.