http://sein-cal.co.cc/
This is our first web application. It is a no-frills implementation of the Seinfeld Calendar, and aids in improving productivity by helping form habits.
We (two of us) started with it 5 days ago. With a bit of Python background, we decided to go at it with Django. The process was in itself a learning experience with remote collaboration, learning and using git to manage the code, and using App Engine with Django. All for the first time.
Feedback welcome.
I'm not sure if it's intentional, but it seems weird that you can't change today's status from completed to "good" to "bad". That make sense for positive goals ("I will do X"), because once you've done something you can't undo it, but it doesn't work for negative ones ("I won't do Y") - since you might end up doing that thing after you've set your status, and want to go back and fix it.
If you're looking for a similar service, check out Joe's Goals (http://www.joesgoals.com/). The interface is nowhere near as nice, but it allows you to have a few goals going at once and track them with more granularity than Seinfeld's initial concept.