I am looking for a personal time tracking software which allows me to set a category (project, task or whatever out is called) for each work item. This categories must be organizable into subcategories (sub projects, subtasks) and I need to be able to get statistics how much work I have spent on each category in some timeframe.
A desktop software (Linux) is preferable, but browser based (self hosted) is OK, too. Open Source is big bonus.