Cannot be ported due to Steam requirement. See comments for details.
Name: Alien Swarm
Website: http://www.alienswarm.com/
License: Unknown (I can't find a license on the website nor Steam pages however the game's source code is freely available. The only license info I have been able to find is at Open Source Living which lists the game as GPL'd.
Description:Alien Swarm is a game and Source SDK release from a group of talented designers at Valve who were hired from the Mod community.
Available free of charge, the game thrusts players into an epic bug hunt featuring a unique blend of co-op play and squad-level tactics. With your friends, form a squad of four distinct IAF Marine classes. Plan your attack using an unlockable arsenal of weapons with countless loadout configurations against a wide variety of aliens. Blaze your way through an overrun, off-world colony, eradicating the alien infestation in environments ranging from the icy planet's surface, to a subterranean lava-flooded mining facility.
Along with the game get the complete code base for Alien Swarm that features updates to the Source engine as well as the SDK. Alien Swarm adds 3rd person camera, depth of field, improved dynamic shadows and a wide variety of gameplay additions to the Source engine.
Notes: The game is initially top down but with a couple commands can be switched to FPS. See here for details.
Doesn't this require steam to play?
Its also HUGE, took me two hours or so to download at home from steam servers.
No, I haven't managed to play it yet, but I'm hoping
Too many lonely hearts in the real world
Too many bridges you can burn
Too many tables you can't turn
Don't wanna live my life in the real world
Yes, it requires Steam, or at least, that is a safe assumption we can make about all Steam games, unless proven otherwise.
Steam is already pretty portable, provided the computers you use it on can connect to Steam's servers. The Steam client itself is not portable, but you can install it on any number of computers, though you can only be signed into one at a time. Sign in on the other computer, and either re-download the game (which is FREE last I heard) or from the first computer, back it up to a portable or external hard drive, and restore it on the next computer.
Steam is pretty cool, but it has no place whatsoever in the PortableApps.com ecosystem. It's not a mark against either, it's just something that doesn't work.
Oh well another one bites the dust. Just have to keep looking forward to a Xonotic release.
PortableApps.com Advocate