Stepper is very simple javascript library that keeps track of a series of steps in a web page. At each step, some code is executed that changes the appearance of the page. Steps are triggered by left and right key-presses, so you can use them to construct a hand-crafted presentation.
Currently Stepper is tightly bound to the excellent D3. It might make sense to break this coupling to allow the use of other visualisation libraries, but that need has not yet arisen.