After trying a number of online project managers for my design and construction business, this one wins hands down for me. This plugin is quite simple but also powerful. It has about all the features I was looking for in a project/task manager. The project users are taken from the WordPress site users list. I can easily navigate between projects, tasks, and sub-tasks. Collaborators can check mark the task when they complete it, and I can un-check it if I want and add comments. After buying and installing, I had a problem with the sub-task feature, but I got excellent tech support impressively fast.
2 MONTH UPDATE:
After two months of heavy use, I love this plugin. I have added the time tracker extension, Kanban, and BuddyPress. I have had minor issues related to conflicts with other plugins, but the tech support team continues to be ultra responsive. Very pleased with the product and service and I hope they continue to improve it.