I can't remember a time I didn't have an idea for creating a time planning / tracking tool. It seems I've used dozens in my life, never finding one that really worked for me. But I've never gotten around to creating one.
In the meantime, I've experimented with GTD. I've come to believe that I don't need to plan my time as before. It's more about tracking for me. Given I have too much to do for the time I have (who doesn't, right?), it seems like I would need to plan. But that planning isn't for each and every task / event. It really is more about how much time I want to spend on each part of my life. Basically, I need to time box my life. And then set goals for how much time I will spend in each box, and use those goals to decide which box I work on next. GTD will help me choose which task from that box.
So, that brings me to toggl. Toggl is a freemium cloud service for tracking time. It has lots of integrations with other cloud services, and apps for iOS and Mac. Perhaps even more importantly, it has an API. So, in theory, I can create an app that simply tracks how I'm doing against my timebox goals. The app could be passive, only showing me how I'm doing when I ask. Or it could be proactive, notifying me when I'm deviating from my goals. And perhaps I could find a GTD backend service to tie to it.
This feels like the future of app development. Don't reinvent anything. Tie together existing services and add a single, unique cherry on top.