I researched Qtask today. Thanks to Sanjeev for the background, demo, and discussion.
Qtask is an secure SaaS-based collaboration and project management environment. It is an online, subscription-based suite of tools. You may compare it to Central Desktop or some focused tools like @Task, weboffice, Daptiv. Some may compare it to Sharepoint but you'd have to actually build and configure Sharepoint to have all the capabilities of Qtask. The one thing I like is that it adds clear accountability to your projects. With only a single Doer of tasks, there is no finger-pointing.

Qtask has been around for 10 years, so it has a well-developed backend infrastructure for secure, online processing and storage of multi-client data. It is now incorporating Cloud storage services to further add to its robustness.

It features all of the typical functions of an online collaboration/project/task management suite plus more.

Point in time:
When you add or replace a person on a project, you can give them access back to a point in time so they can see all or portion of the project history.

Discussions are logged and can be created around any type of object such as a topic, task, or even a calendar event. Turn the discussion into a Feed so others can subscribe via RSS.

Files are tagged by project. Each project has its own hierarchy. Includes VERSIONing - Yea.

Create Checklists for your own Compliance - assigned to Doers to perform on a periodic basis.

Qtask Integrated Services:
Information Sharing: Feeds, Forms, Wikis, Files
Project Management: Scratchpad, Contacts, Calendar
Communication: Discussions, Mail (Integrateable with your Outlook)
Project Management: Dashboard, Reports, Tasks, Compliance