Todobot is an online todo list manager. It started because I needed a way to manage some todo lists (that was better than editing a text file on my hard drive), and I thought it might be useful, so I decided to have it support other users as well. The implementation is in PHP, with a MySQL DB holding the important stuff. It will eventually be open sourced, but I'm not happy with the code right now. However, if you don't trust me and want to run your own copy, send me an e-mail and I'll be happy to send you what I've got so far.
Todobot requires no password for two reasons. First, everyone can remember their online handle (or first name, as it happens), and nobody wants to remember another password. Second, I thought it might be useful for users to edit each others' todo lists (e.g. add something, or check something off to prevent redunant work). If you decide to be mean, I'll hit you in the face with the banhammer, so please don't. If there's too much abuse, I'll just add password support. That said, I don't think todo lists are very sensitive things, and so I don't think this will be much of a problem.
Also, if you find a bug (or you have a suggestion), send an e-mail to me (my contact info can be found on my main page). Hopefully todobot is useful for you!