Did You Mean? is a Redmine plugin I wrote with Mattia to warn users before they enter duplicate issues, in an attempt to mitigate issue tracker misuse. It was inspired by the way Stack Overflow handles the insertion of duplicate questions.
The plugin is designed to warn users before they enter duplicate issues and it does so by performing a search among the existing items right before users submit new ones. Search is based on the issue subject and it is done in the background, in an attempt to make the process as effortless as possible to users.