It's a Jupyter kernel, so that you can run C code from a Jupyter Notebook in your browser, like you can with Python, R, etc.
It's similar to a webpage that posts C code to a web service and returns the output of its stdout (so like CGI). Not that this is a bad thing, but when I read about stuff running in the browser, I suppose the code to be run by the browser itself, and not just visualizing the output of a program run on some remote server.