This branch is no longer active, however check out the version 2.0 rewrite maintained by Yanick Rochon.
This is a more advanced but not well tested extended version of the jQuery UI Multiselect widget.
It just got updated to work along with jQuery 1.4.2 and jQuery UI 1.8.
I’ve installed a demo page at http://quasipartikel.at/multiselect_next/
If you have suggestions or did some nice modifications just let us know.
We’d be happy to review them, and perhaps include them.