I wish something existed in this space. I used Coati Software's Sourcetrail for a couple of years. Unfortunately it was discontinued. It was a wonderful piece of software that indexed a code repository, and exposed an interface to explore it interactively. At least for me, it significantly improved the understanding and legibility of code.

The code is in an archived state (https://github.com/CoatiSoftware/Sourcetrail). Searching for the software on Google shows some screenshots.