From Takayama Fumihiko:
Karabiner (formerly KeyRemap4MacBook) is an awesome utility for keyboard customization for Mac OS X. - You can re-map any key without any restriction. - You can accelerate speed of the key repeat. Karabiner offers frequently used settings. You can activate them by simply clicking the checkbox in the list. If the settings which you want are not in the list, you can add them by yourself. Karabiner has many useful features for efficient keyboard operations. You can do Emacs-style operations anywhere. You can do Vi-style operations anywhere. You can do Mouse operations from keyboard.