How to get it

If you're on Windows just hit your Windows key + R (or simply go to "Run" from start menu) then enter "steam://install/480" while you're signed in on the Steam client.

This was a old demo game for Steam to show off some features such as achievements.
It's free but I don't know if all the achievements are unlockable.

Can the 2 multiplayer achievements still be unlocked? We can't seem to find each other's lobby or server with my friend.