Toribash
It's not free anymore to people who didn't already have it on their steam account, but if you had a subscription before the standalone client was deprecated you can email support and they'll help you sort it out.

Brilliant game, extremely high learning curve but well worth getting into. Here in Australia we have a couple of full servers running every single night, mostly with people playing Clan Arena (both vanilla and turbo modes) at all skill levels and it's hella fun.
Hands down my favourite game to play, and easily worth $10 IMO, but it will probably take you a few weeks to stop getting destroyed by even the relatively new players unless you're already good at another arena FPS.
Highly encourage people to pick this up - now that server hosting is in the community's hands and with minqlx, there's a ton more stuff that we can do - including host custom maps again! If you'd played it previously but not really gotten into it, it's improved a TON over the past couple of updates and (again) it's hella fun to play.