A way for the Command+TAB app switcher to continuously cycle instead of stop at the end
Even as early as Lion, command+tab when held continuously stops at the end and does not cycle. Releasing the tab key and then pressing it again resets the cycle to the beginning. It is not necessary to release command. Releasing taband then pressing shift+tab will reverse scroll through the app listing.

To the very best of my knowledge, this behaviour is hardcoded and not configurable by the end user.