My friend Alex King has released Tasks Pro 1.1:
Tasks Pro™ is the multi-user version of Tasks: a powerful web-based task manager (to-do list manager) that allows you to organize your tasks in a hierarchical structure. Group controls allow projects to be set up only for people who need to see them. The easy browser based interface lets everyone in your groups work together easily and efficiently. The Tasks Pro™ server component is cross-platform compatible and can be installed on any Windows, Mac OS X or Linux computer running PHP and MySQL.
I've used it for my own purposes, and highly recommend it.