Not exactly a module, but a site that's useful for module authors. I need some reviews before I blog about it.
This website lets you track changes to your favorite modules. It serves RSS feeds for separate modules, or (if you log in) you get to set up your own group of favorite modules, and create a custom RSS feed consisting of them.
Each feed item contains the new lines from the module's changelog, so you don't need to visit the module's page to see what changed in each new version.
The idea behind the project, is that people whose projects depend on a lot of modules, will be able to see easily & quickly whether one of their dependencies has some new exciting feature and is worth upgrading.