Active Collab Alternatives for Linux

Redmine is a flexible project management web application.

Trac is an open source, Web-based project management and bug tracking system.

Mantis Bug Tracker is a free and open source, web-based bug tracking system. The most common use of MantisBT is to track software defects.

fluxday is a user-friendly, free & opensource task & productivity management tool for growing startups.

Ora is a real-time all-in-one workspace for teams.

GanttProject is free Java based, project management software that runs on the Windows, Linux and Mac OS X systems.

Avaza is a beautiful online software suite with modules for Project Management, Timesheets, Expenses & Invoicing. Access from anywhere, with any device.

Phabricator is a suite of web-based software development collaboration tools.

Bitrix24 is a free (for small businesses) social enterprise platform.

Drupal is a free and open source content-management framework written in PHP and distributed under the GNU General Public License.

LibrePlan is a free software web application for project management.

PMRobot is Project Management Software designed exclusively for Software Consulting Companies.

Tuleap Open ALM is a libre & open source platform for agile management and software development.

FogBugz is an integrated web-based project management system featuring bug/issue tracking, discussion forums, wikis, customer relationship management, and evidence based scheduling.

GNOME Planner is a cross-platform project management tool based on the Work breakdown structure (WBS).

Rachota is a portable application for time tracking different projects.