How to find all Drupal modules which has dependence I would like to know if it possible to find all contributed modules that depend, for example, on the Subform module.   

This information could be useful if you are working with a module, and want to create yours because you don't know that the same module already exists.
That's really easy to do with Gotta Download Them All. Once you have downloaded all the modules, you can just run a grep command to search the whole contribution space.