The first horror game is Amnesia: The Dark Decent, which is a psychological horror game that we've written about before. You hide from terrible things that are actually creepy and it really is one of the scarier horror games!
The second is Limbo, a dark platform game full of many many deaths! You find yourself up against a range of disturbing scenarios as you travel through a foreboding monochrome world.
The other games contained are Psychonauts, a platforming title from the maker of Grim Fandango, and Superbrothers: Sword & Sworcery EP, which is an adventure game.
The idea of the humble bundle is that you can pay any amount from $0.1 to $100000 and will receive all the games. You can decide how much goes to charity, to the developers and to the humble bundle makers. But if you give more than the average of what other people have given you receive a bonus game (this is currently $7.71). This time the bonus game is Bastion.
All of the games will work on Windows and several other varieties of PC, and can be bought from any country worldwide (the prices are in dollars, however).
For more information go here!