Well, to call it a to-do list is really a big understatement. It's a fully fledged GTD system, that integrates seamlessly with Evernote (in addition to the normal GCal integration), both for inboxing and archiving. If you're a GTD fan and you use Evernote as your primary way of capturing information, Zendone is basically unbeatable.
And yes, I use it myself, every day.
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