Co-operative multiplayer game and complete code base available for free.
Alien Swarm is a free action game released under See Steam store page. It runs on Windows, needs about 2.0 GB of disk space, and requires no account, payment or trial. On a computer, the fastest route is the PlayBound Launcher. On a phone or tablet, use the official store or site instead.
One-click install
PlayBound fetches the official release — no third-party mirrors.
Windows
Choose Install in PlayBound. Steam opens the free Alien Swarm app (630) — sign in if needed and let Steam finish the download.
Windows
Return to PlayBound and press Play. For controllers, use Steam Input or the game's documented 360controller console exec; Reactive Drop is easier if you want official full pad support.
Minimum
Windows 7 / Vista / XP · Pentium 4 3.0 GHz · 1 GB RAM (XP) / 2 GB (Vista+) · DX9 GPU 128 MB SM 2.0 · 2.5 GB storage
Recommended
Windows 7+ · Core 2 Duo 2.4 GHz · 2 GB RAM · DX9 GPU SM 3.0 (GeForce 7600 / Radeon X1600 or better) · 2.5 GB storage
Yes. Valve released it free on Steam. PlayBound hands off to Steam for download and updates — there is no separate PlayBound-hosted package.
Alien Swarm is Valve's original 2010 campaign. Reactive Drop is the free community continuation with more content, active multiplayer, and official full controller support. Both are listed separately on PlayBound.
Partially. Classic Swarm often needs Steam Input or console commands. Reactive Drop ships official full controller support.
The campaign supports local play with bots. Online co-op needs Steam and a network connection.