Mark Bernstein has a long post on the concept of a personal Daybook kept in Tinderbox. It's not immediately clear to me whether he is talking about an actual product made in/for Tinderbox, or if he is just theorizing. Either way, it sounds fascinating, and I want one. That and the ability to synch Tinderbox with my Palm.
Update (2/20/04): Mark has cleared up my confusion: his Tinderbox Daybook is not only an extant application but also incredbly simple to implement (it really sounded more difficult the first time). Definitely worth investigating further.
How 'bout the Palm synching, Mark?