If you own a Tablet PC, or a UMPC, or even if you have a desktop PC with a graphics tablet and the tablet extensions enabled, this app is a must-have:
InkSeine truly reinvents the pen-based input paradigm, and shows what's possible with a tablet PC. Write notes in ink. No big deal, you say? Lasso your notes and search either the web or your local machine for the lassoed phrase. Drag shortcuts to web search results or documents directly into your notes. Use gestures to control the application, rather than menus. And lots more.
One of the really cool pieces of InkSeine is the Tool Ring, which provides constant shortcut access to scrolling, zooming, and screen shot capabilities. Read more about the Tool Ring here.
CAVEATS: It's beta software, and it's not an official Microsoft product (it's from MS Research), so if you're not cool with beta bits, it's not for you. And it does have limitations. But wow, is this a nifty application.