Is an excellent plugin for Scrum support. Homepage, old forum thread, new forum link.
To install Backlogs, clone into your plugins directory the repository from:
https://github.com/backlogs/redmine_backlogs.git
Then run the db migrations:
bundle exec rake db:migrate RAILS_ENV=production
To remove Redmine Backlogs, run the migrations first:
rake db:migrate:plugin NAME=redmine_backlogs VERSION=0
RAILS_ENV=production
and then simply delete the plugin directory (redmine_backlogs in plugins).