I use Steam for some F2P games (Wakfu recently got a Steam release, I'm going to see about figuring it out soon). I have Quake Live. It's obvious that it's based on the ioquake3 engine. Not that that's necessarily a bad thing: it makes it comfortable to run on an Intel HD chipset, after all. A surprising amount of games support the Intel HD - I run Fallout 3 and New Vegas at my native res, and although I have everything else set to low, it all runs at a playable frame rate. Surprising when I can barely get Skyrim playable at 640x480. I tried the "Ultra-low graphics mod", and while it helped significantly my framerate at 1366x768 was unplayable.
I'm guessing you all know about the Doom sourceports, like GZDoom, Doomsday, jDoom, etc.
How does a good old deathmatch sound? I'd love to get brutally murdered by you guys in a pseudo-3D map. I use Doomsday, and I'll see about details of configuration later.
If you have the Doom wad it can play it. It also plays Doom 2, Heretic, and Hexen.
Let me know when you're free, and I'll see about clearing that block of my schedule. My time zone is EST, but if I'm really quiet my parents don't care (or know, really) that I'm up into the wee hours if that's what it takes. Sleep? I don't need sleep. I run on pure spite.