I'm crawling some famous C repos at GitHub for VersionEye. There are listed here: https://www.versioneye.com/C. And I integrated the biicode, a dependency manager for C/C++. The biicode packages are listed here: https://www.versioneye.com/biicode. Currently there are no tags like at libraries.io but maybe I will add tags and tag filters for browsing tags/categories.

This is where https://libraries.io/ falls short. While the execution is really great (good job), the idea that a developer might be looking for projects in a wide variety of language/platforms at once is false.

Most of the time you already know the platform and want only to search for this platform, not all of them.

It must be a fun project to do still.