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

Redmine 5.1 introduces these new features in these categories:

* Migrate to Rails 6.1 with Zeitwerk autoloading.
* Introduced CommonMark Markdown (GitHub Flavored) formatter as an
  alternative to existing Markdown formatter based on Redcarpet.
* Users can be mention now using @ autocomplete by other users with add
  watchers permission.
* Issue custom query: default query per instance, project and user.
* Default project custom query: per instance and per user.
* Ability to add watchers to Wiki pages.
* Issues can now be filtered by notes or by file description.
* "Contains" operator supports now multiple search items.
  Using wilcard characters (_ or %) is no longer supported.
* Two-factor authentication improvements: you can enable it only for certain
  groups or for users with administration rights.