Free, tactical, unforgiving. The mod that started the Insurgency series.

Free, ridiculous, John Woo on Source engine. Dive, flip, shoot.

Free Wild West shootouts on Source. Slower guns, same instinct.

The one that's actually still free. If you haven't touched it lately, that's on you.

Free survival-horror multiplayer, old Source bones, still tense after all these years.

Free, Source-engine, co-op zombie fragging. No microtransactions, no catch.

Free, tense, Source-engine co-op. Different genre, same "still worth booting up" energy.

Not a deathmatch game, but free, Source-engine, and still holds up.

Free, huge, still the standard. Different game, same instinct.

Free-to-play, modern Quake, same DNA. Not QWTF — but the itch is adjacent.