Apocalipsis creeps me the hell out (opens in new tab). It's a point-and-click adventure game filled with giant fish, musical instruments made of human bones and a young boy with eerily long fingers—and it's just come to GOG sporting a 40% discount.
GOG's DRM-free version (opens in new tab) is the Wormwood Edition, which bundles the game with its story DLC One Night in the Woods and an artbook. It also comes with the soundtrack, which was made by Polish metal band Behemoth, and lead singer Nergal narrates the game.
The $6 price tag, which includes the time-limited discount, is the lowest the Wormwood Edition has sold for. The base game, which came to Steam last year, has gone as low as $3.50 on Steam (it's currently $7 by itself)
Apocalipsis is definitely not for everybody: it has some terrible action sequences, the puzzles aren't particularly clever and the environments—although packed with detail—can feel plain because of the muted color palate. But if you're into surrealism and Dark Age imagery, it's definitely worth a look. Check out the trailer here (opens in new tab) before you make up your mind.
If you're interested, you can buy it from this page (opens in new tab).