The wonderful website Pixel Prospector turned three yesterday. To celebrate, they cooked up this very useful little video called 44 Free Indie Games In 4 Minutes (Multiplayer Edition). Which pretty much sums it up.
These games are all on PC and all available right now to not only play, but play and enjoy with/against another human being.
For a complete list of every game included, head to the link below.
44 Free Indie Games In 4 Minutes (Multiplayer Edition) [Pixel Prospector]