At VersionEye you can take a look which other open source projects are using a certain open source library. We call that references. If for example log4j is using the JUnit library, then log4j is a reference for JUnit. On the detail pages of each software library you can see how many references a software library has. This is how it looks for JUnit.
JUnit has more than 55K references. That means more than 55K open source projects are using JUnit as a dependency.
By clicking on the number you get all of the references listed. That’s not new, but now the list of the references is sorted by their reference number. That means the open source library/reference which has the most references is on the top. This is how it look for the JUnit reference list:
The most popular open source library which is using JUnit as a dependency is slf4j-api. Because slf4j-api itself has more than 17K references from other open source libraries. In the list of the JUnit references it’s the open source library with the most references.
The references are available via the VersionEye API as well.