A ToDo/ task list

Hi ppl, I have been thinking of using PHP to make a ToDo/task list type of application. I am looking for something different from the usual Personal Information Managers (PIMs) - they are oriented more towards appointments than tasks. Does anybody know of any ongoing (preferably open source) projects in PHP of a similar nature? I would like to be able to open/create a task, maybe assign it to somebody, be able to add comments to it, have user authentication and the most desired (though uncommon) feature is: a change log. Through a change log, I want to be able to trace the who and when of comments added to a task etc. Any help/pointers will be highly appreciated. Thanks, -- Regards, Harshdeep Singh Jawanda.