Synergy is a community made mod for Half-Life 2 that allows you to play through the campaigns with your friends:
Half-Life 2
Half-Life 2: Episode 1
Half-Life 2: Episode 2
Re-live the epic adventure/nightmare as Gordon Freeman against the Combine republic! Experience silly gravity bugs and interesting effects while solving puzzles and goofing off with the gravity gun! Its endless fun!
Helldivers is a 3rd person twin-stick action shooter with upgrades, co-op and medium sized maps with missions. One interesting element is the online players help each other overcome enemy solar systems by completing objectives on each planet. If you play co-op with 3 friends and complete all the planets in the solar system, then online players no longer get to play these maps until all of them are complete. If your team dies and you quit the game, other players can try the objectives...
Magica is a unique and original sandbox action game with 100s of spell combinations in a co-operative wizard of magic and comedy. There is no other game like Magicka! This is no typical dual-stick or RPG this is magic chaos at its best!
Use QWER & ASDF keys to weild water, heal, sheild, ice, shock, death, earth and of course... Fire!
But the real trick is to combine these elements by loading up to 5 slots of available spell combinations. The results are...
Assassin's Creed Unity takes place in France during the French Revolution. Make your way through the streets alone or with 3 friends and free the lower class from oppression by assassinating key figures in power. Purchase costumes, gear, skills and even co-op boosts to complete the single-player campaign or co-op missions.
Dungeon Hunter is a mobile RPG series that is completely free-to-play. Fight in an epic story in singleplayer campaign or play co-op with 3 friends in all kinds of beautiful war-torn environments in Valenthia. Wield hundreds of weapons, armor and spells... fight in tower defense modes and take on daily events.
Island Saver is a free-to-play first person clean-up game where you are saving the island from litter bugs who want to pollute it. Wield your Trash Blaster and suck washed up plastic and recycle it. Then suck up water can and clean the black goo from trees, water and recycling objects which help you clean up the island.
This is an absolutely kid safe game! And its educational by teaching kids how plastic and pollution can damage the environment and an animal ecosystems. Once you complete...
Left4Dead 2 is a zombie apocalypse co-op shooter made by Valve with the Source engine in 2008. The story follows 4 people who are trying to survive zombie hordes with a movie-esque cinematic feel like the classic horror movies. Enjoy slaying all kinds of zombified humans and special mutated monsters with classic weapons like machetes, pistols, shotguns, UZIs and much more!
Play co-op with friends or solo with 3 bots and hack your way through running hordes of zombies to the safe house....
PREY is an absolute "Must Play" if you are a first person shooter gamer! Imagine System Shock 2 on steroids with amazing graphics, clever morphing aliens, psionic abilities, loot, crafting, survival, sneaking and more. Of course all happening on a space station! Doesn't get any better than this!
