On GitHub, how can I find the repositories I have forked but are still identical to the parent repository (i.e. no changes were made in the fork)?
Painstakingly and one by one.
There isn't anything to show you at a glance all your project forks which share the same commit revision history or are different in some way to the original repo.
For each of the original repos you want to compare against, click on their respective Network Graphs at the following URL type:
The original repo will be at the top (base reference point) and list a few other repos in timelines below it. All branches and commits are marked out in the first line. Any commits or branches that forked versions contain, but are not in the original, will show up as competing racing lines in the graph.
Example network graph
original-repo |---*----*----*----*------------*--*-*----------***----*- | | toothygrinmeister | |--------* | | cuddlebucketeer | |------*--*-*
In this example, both toothygrinmeister and cuddlebucketeer have commits that original-repo does not. Should either one of these users issue a pull request and their code is rolled back into original-repo, then the respective dots on the graph would disappear.
Similarly, if your fork does not appear on the network graph when viewing against the master as the zero point, then you can assume your fork is up to date and matches that repository's commit history.