osu - a rhythm based game, hard to learn, easy to master, like toribash.

powder toy - i download this on school computers, its a pretty cool game

any old cd rom games - i recommend spiderman 2000, frogger, and simcoaster/sim theme park.

Funny that no one mentioned League of legends.
Free to play game that can run on almost any computer.

Dota 2 is better :v

Dota 2 is shiet. No offense to people that play Dota.

i know what you can play

1.Download an arcade emulator and get any of the ol good street fighter games.

2.M.U.G.E.N Runs on any computer.

3.any of the command and conquer games.

4.toribash(duh)

5.halo

SanctuaryRPG

can't believe Rimworld only has been mentioned once, great game that I'd highly recommend (and it runs on low end pcs ofc)

Broforce
Any game by Telltale, these even run on a cellphone
GTA San Andreas, that samp is still fun to play with friends
Rayman Legends
Paladins
Team Fortress II
Dishonoured, well optimised for pc
DmC, same
Dark Souls II, same
Batman: Arkham Asylum

And try to stay away from recent open world games, they need a good computer to run in playable fps.

hyper light drifter

risk of rain

downwell

axiom verge

shovel knight

spelunky

any 2d pixel art indie game really

Wonder boy, did this game like a shit tons of time long time ago. They have made a remake version few months ago and it's cooooooooool