Plan9Pro, open source, 9.99$

Plan9Pro http://itunes.apple.com/us/app/plan9pro/id446279511?mt=8
Plan9 http://itunes.apple.com/us/app/plan9/id432571698?mt=8
Plan9Free http://itunes.apple.com/us/app/plan9free/id435026648?mt=8

Plan9 is a TODO manager. This app contains the source code.Unzip the app and find the plan9.tgz package.
You can do anything with the source code.