Collabtive is a free PHP project management software with a Web 2.0 looking, ajaxed interface.

The software is still in the beta phase but it already has the features like:

• Projects, Milestones, Taskslists, Tasks
• User management
• Message system
• Integrated instant messenger
• Multilingual
• Template system

Activecollab was one of the most popular free project management softwares that became a paid solution after sometime. If you are looking for an alternative which will run on your servers & have an open source code, take a look at Collabtive.

There are some nice upcoming features like a flash progress meter for the projects.

Redmine is a flexible project management web application. Written using Ruby on Rails framework, it is cross-platform and cross-database.

With a plain interface which makes the use easier, Redmine has most of the features a project managemnt software must have like multiple projects, role based access control, wiki & file management.

Redmine features:

• Multiple projects support
• Flexible role based access control.
• Flexible issue tracking system
• Gantt chart and calendar
• News, documents & files management
• Feeds & email notifications.
• Per project wiki
• Per project forums
• Simple time tracking functionality
• Custom fields for issues, projects and users
• SCM integration (SVN, CVS, Mercurial, Bazaar and Darcs)
• Multiple LDAP authentication support
• User self-registration support
• Multilanguage support
• Multiple databases support

Redmine is in beta status yet and improved regulary.