There are some of plugins, which provided very interest abilities, but some of them are unmaintained for ages, some didn't work with Rails 5 or have a bugs. All of these didn't work with Redmine 4. These plugins relatively small, but can noticeably extend Redmine functionality.

Please import their main abilities to base Redmine project.

There are:

• Redmine LDAP sync https://github.com/thorin/redmine_ldap_sync
  Provide ability to sync LDAP/AD users with Redmine without requiring they to login at least one time. This way project manager can assign tasks to users immediately. Plugin installs, but server didn't start, throw an error. Very usable plugin IMHO.

• Redmine login audit https://github.com/martin-denizet/redmine_login_audit
  Provide ability to account and view login attempts into a Redmine. Extremely useful for Information Security (i.e. for me :) ). Plugin didn't install.

• Add subversion links https://github.com/masamitsu-murase/redmine_add_subversion_links
  Provide ability to change simple mention a SVN commit to link to repository page, where you can quickly browse their content. Didn't install, require Rails 4.

• Extended watchers https://github.com/maxrossello/redmine_extended_watchers
  Provide an ability to change original access mode to mode "notify about changes in task, regardless by inclusion in the project". Project can contain tasks, which mustn't be available to some users, even their name! With provided by this plugin "extended" access system, I can add user to separate task - and he can view it and receive notification, but he cannot view any another tasks. This plugin install, but server throw errors about "stack level too deep" when I try to add any project.