AgileTask is a lightweight personal backlog tool. Agiletask is a task tracking application featuring an agile workflow, tagging for organization, and interesting achievements. Designed to bring some structure to your Agile projects, and help you stay focused on what is most...
Anxiety is a super-lightweight To-do list application for Mac OS X Leopard that synchronizes with iCal and Mail. Its aim is to provide a streamlined, easily accessible interface to add and check off your tasks, while remaining poised to melt into the background at a moments...Discontinued
Official site unavailable but download still available at download sites.
OpenLoopz is a task management system with a difference! It is inspired by Getting Things Done by David Allen and uses the special features of the Android system to make task management easy and fun!