Ruby Tracker: An Online Dependency Tracker for your Ruby Projects
Ruby Tracker is a new webapp from EnvyLabs that tracks dependencies for your Ruby and Rails applications. It alerts you whenever libraries you depend on are updated or have new versions released. This is all in aid of keeping up to date.
Only two downsides: Ruby Tracker only works with projects that use Bundler and that are in an Internet-accessible Git repository (such as on GitHub). It can deal with private repositories, however, so your code doesn't need to be publicly accessible.
In true Envylabs style, a screencast explains how Ruby Tracker works:
Nathaniel Bibler has written a blog post explaining what Ruby Tracker is all about in case the idea doesn't click for you immediately.