We're looking for an open source or low-cost Web-based project management tool. The most important feature we need is a decent calendaring system that will work with users from distributed groups that don't share an e-mail platform. We would like the kind of functionality Outlook provides for calendars and tasks in an Exchange environment, but without requiring that everyone use Outlook and Exchange.
There are several free and low-cost project management and collaboration groupware tools, ranging from full-featured project management portals to simple task trackers, or software tool kits that interchange information and data files between open formats and Microsoft Project.
It sounds like some general content-management systems will provide calendaring features to meet your needs. The Open and Free Project Management Tools site provides a list. Take a look at dotProject, Tutos and Trac.
DotProject is a PHP/MySQL Web application that delivers project management, task-tracking and calendaring tools. Straightforward Web-based installation requires only a MySQL database and a user with privileges to create a database.
Tutos is similar to dotProject, but a bit more difficult to install, and has a more mature documentation base.
Trac is interesting because it is wiki-based, which makes it more flexible for distributed and diverse workgroups.