Redmine

Redmine has been running in production since 2006, which makes it the most battle-tested tool in this entire category — nearly two decades of continuous use across IT departments, universities, and enterprises that value stability over novelty. It supports multiple projects with independent roles and workflows, native Gantt charts and calendars, custom fields on issues/projects/users, and direct repository integration (SVN, Git, Mercurial) that links commits straight to issues.

One quirk worth knowing: Redmine's own bug tracker and primary source repository live on a self-hosted Subversion server at redmine.org, not on GitHub — the GitHub repository is an official read-only mirror, so its low open-issue count reflects mirror activity, not the health of the project (Redmine's real tracker has thousands of open tickets and an active core team). The plugin ecosystem built up over Redmine's lifetime is enormous, covering everything from agile boards to time-and-billing to helpdesk workflows.

The honest downsides are exactly what you'd expect from software this old: the interface is dense, configuration-heavy, and dated next to Plane or Huly, and there's no kanban board in Redmine's core at all — you need a plugin (commonly the Agile or Backlogs plugin) to get one. Core development also moves slowly, with most real innovation happening in the third-party plugin ecosystem rather than the base product. For an IT department that needs something that will still be running, patchable, and supported a decade from now, Redmine's track record is unmatched. Teams that want a modern UI out of the box should look elsewhere.