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.