You may not have heard of reQall. And if you have, you probably think of it as a service for sending reminders to yourself by phone. But it's also a shockingly usable to-do list system (and a whole lot of other things).

Here's how the note-to-self thing works. When you call the reQall phone number, a recorded voice gives you command options. If you say the "Add" command, the phone beeps, and you leave a message. It's like calling someone's voice mail. When you're done, hang up -- reQall takes your spoken message and converts it into text. It then e-mails that text to you, and also adds it to your to-do list, which lives on the reQall Web site.

When reQall's number is on speed dial, the process of entering an item into your GTD to-do list system is: Press one button. Talk. Hang up.

That's the most minimal and widely known use of reQall. But the service also has an extraordinarily powerful, simple and GTD-compatible system for managing action items. The basic view shows "Today," "Soon," "Overdue," "Later" and "Shared Reminders" tabs.

When you call in a reminder, new items go into "Today" by default. By clicking on an item, you can see its completion status, what folder it's currently in, a "when it needs to be done" item and a "who needs to do it" option.