Recommended by JefRaskin (in TheHumaneInterface) as a replacement for MouseMode selection/designation of cursor position. Requires 1 or 2 extra ThumbButtons on the keyboard. The suggestion is that they be centrally located to the left and right of the space bar and operated with the thumbs - approximately where the "Windows" keys are on a current keyboard, and labelled "Leap Up" and "Leap Down". LeapMode is supposedly more efficient, since it avoids having to move your hands off the keyboard to do navigation, as in MouseMode.
They would act as sort of meta keys, triggering an incremental search (such as C-S does under EMACS).
Within a wiki this would be nice, since pressing a LEAP key would let you switch focus to the summary field, save and preview inputs when you finish your text entry. (there is no keyboard command I can find to let a user break out of a text entry box in Mozilla).
This is different from using Tab/Alt-Tab to cycle between links or form elements; as well as spelling the link you want to jump to in Mozilla; as well as providing accelerator keys to jump to a particular link or form element because there is LEAP (next word), double LEAP (next paragraph), triple LEAP (next page), and then meta LEAP (next search), and so on. LEAP is only the actual button on the keyboard; it keys to many different functions that are all conceptually related to navigation.
LeapMode was implemented on the CanonCat.