There already had been a Tooltips implementation but i wasn't to happy with that one, not only because they didn't support simple mouse-hover tooltips - actually they do.

But writting this lib was also a good way to get into script.aculo.us and prototype.js. (and i can't say how impressed i am)

So here it is:
An all new Tooltips.js
http://static.twoday.net/matsblog/stuff/Tooltip/Tooltip.Demo.html

Source available via:
http://static.twoday.net/matsblog/stuff/Tooltip

Currently the script has version 0.3 and depends on some changes in script.aculo.us and prototype. My goal is to get a version 1.0 released, that is compatible with the next scriptaculous realease. In the meantime i would be happy about any feedback and/or testing.

Please dig into the code to learn, what the various actions do.

The basic structure is:
* Tooltip Class
(representing a single trigger-popUp pair,
handles setup/show/hide)
* TooltipFactory Class
(provides a framework for finding and initializing tooltips
in a site by finding them via style selector)
* Tooltips, ActionHints, SectionTriggers
which are implementations of TooltipFactory
-> This is the most interesting part, if you want to use tooltips
or want to implement your own flavor of tooltips.