Tracker Checker is Windows only and requires the .NET 2.0 framework. It will regularly check the signup pages of the trackers you wish to join and notifies you when one of these is open to newcomers.
The program currently supports 66 private trackers. If your favorite tracker is not in the list you have the option to add it manually in the “trackers.xml” file. The application is spyware and malware free. It does lag a bit when it checks the trackers, and some of the URLs are outdated. My suggestion would be to set the refresh interval to a couple of hours or even more, or just run the program occasionally.