Warframe is free to play, just had a major update, and the community that I've seen is pretty inclusive. It's also pretty addicting.
Comradeship // Freechat
Talk about whatever, respecting the rules established by Lemmygrad. Failing to comply with the rules will grant you a few warnings, insisting on breaking them will grant you a beautiful shiny banwall.
A community for comrades to chat and talk about whatever doesn't fit other communities
Nethack. :D
Dwarf fortress, ASCII only 😈
Fallout New Vegas, although you probably played that one already. If you are more into competitive MP then I can't think of anything where you inevitably wouldn't run into that sort of problem, which says a lot about the state of game communities these days...
Minecraft
ARK
xonotic would fit in the sci-fi fps category you mentioned one time. same with red eclipse (on steam)
both are foss
WAIT WAIT, play openra. openhv as well. some bit of stratergy
want a bit of elder scrolls? openmw for that morrowwind goodness
How much money do you have? If you don't have a lot I have a TON of free games you can play
I'm going for games under $50, but I'll take Free to play also
Just a Humble Swordsmith, Cyrah's Ascent, Paper Wizards, Fly Dangerous, Prosperous Universe, Hip Witch, Plasma, Never Split the Party, Rawbots, Exhibitors, Deceit 2, Conjury Revell, Klaus Veen's Treason, King's Quest, NOVA CORE CHAOS, SoulBound, STRATAGEM, Veiled Tales, Beyond the Breach, The Summit Library, This Magical Girl is a B☆tch, Inversed, It Paints Me, Familiar Friends: What's Your Familiar?, Adequately Ever After, Sarpedon, SUPERVIVE, IMPACT, Just War Trains, The Eminence in Shadow: Master of Garden, Escape From Castle Matsumoto, Compactory
All free :)
db sparking zero! fite me
Are you into strategy? Anything ranging from Age of Empires, Total war, Civilization etc.