You may recall iGTD, which we covered last year. Up until some Leopard difficulties forced me to start flailing between not-quite-ready GTD applications, I was a loyal user. And yes, those Leopard difficulties could have been solved, but the author had his hands full with reincarnating iGTD -- as iGTD2. iGTD2 is in alpha right now, and not what I'd consider to be trustworthy for daily use, but it provides a peek into the thoughts behind the revamp.
Whereas the original iGTD started out fairly simple and grew increasingly complex in response to user requests, iGTD2 is starting out quite robust and tries to get a grasp on what people really want out of their task managers. But, like the original, flexibility is built into the system. This time around, the authors developed a set of "principles" to guide development and make a simpler task of creating a new UI. Some of the principles are quite simple: a need for tabs, a hatred of inspector palettes, and the need for more mouse-friendliness. Some of the ideas, though, are a little more rebellious against the standards of GTD and delve into new ways of approaching task organization and, well, getting things done. Tags, focuses, nesting tasks and other UI developments allow for flexibility beyond what you'd expect from a GTD app.
This kind of flexibility might be annoyingly overwhelming for new users. If you're looking for a simple UI and straightforward task manager, this probably won't be it. But if you've ever craved the ability to archive links and notes and then attach whole groups of them to projects and tasks, iGTD2 is moving in the right direction. As of this writing, the iGTD2 alpha is on its 9th build, with major changes happening almost every day. This one is worth keeping an eye on, especially as a donationware offering that will likely rival the power of some of the commercial applications in the field. The alpha is available for download and there's a forum for user input. If you're curious, check it out!