The (traditional p&c) adventure genre sells very poorly these days, despite having a loyal following. Unfortunately since they tend to have awful sales, publishers are incredibly skeptical of new adventure games. Double Fine decided to try to fund a game with only money from fans. Donating certain amounts can give you rewards (such as a copy of the game on Steam).
Double Fine's goal was to raise $400,000. They still have 27 days left and they've already managed to get almost two million dollars. The game has plenty of money now, but there's still reason to donate. After all, the rewards are still available and they plan to use all their excess money to make the game even better (and to port it to other platforms).
This was a brilliant idea. The problem with cult classics is that everyone pays the same amount. This discourages appealing to niche markets. However, with a platformer like kickstarter a fan that would have only payed $60 (at most) normally might pay obscene amounts of money (one person donated ten thousand dollars to Double Fine's game). Adventure games are my favorite genre, so I'm very happy to see this happening.