http://www.backpackit.com/I've been playing with this application for a couple of hours, and it's pretty neat. At first it seems too simple to be useful, but after a while I'm getting into the swing of it. Basically, you can set up pages (only 2 on the free account), and on each you can create lists, notes, and "writeboards" (notes with formatting). You can publish pages individually if you want others to see them, and each page has an email address that you can use to send todo list items or notes to.
That's about it really. I'm actually finding it about the right level of complexity (simplicity) and structure (lack of) for what I need. I may end up getting a paid account if it's still doing it for me in a few days.