I would like to be able to automatically run a script, when a certain event happens (such as, a file save), depending on the file-extension (and maybe also depending on the project).
For example, what I really like to do: If I save a file that ends in .rb, I want to automatically run a command that does a "ruby $TM_PROJECT_DIR/test/unittests.rb". If it fails, it could send me a notification through growl (http://growl.info)