Note Studio is a Win XP / Palm wiki application. It gives you the ability to use and maintain personal wiki applications on both platforms. Very handy if you want to keep your notes and data in one place rather than scattering over several different applications on different platforms.
Update: As of 08/2006, the current version is 3.2.2, which includes some interesting enhancements including the ability to embed checkboxes in NoteStudio pages that can be checked off on both the Palm and desktop. Versions are available for both Windows and Mac.
Update: The current version is 3.1.1. There is also a Mac version in Beta...
Update: NoteStudio is extensible with python files, and one is available to make a GTD Next Action list, by context, by scanning all your pages for links like [@Call] and [@Work]