There are quite a few alternatives, microhttpd is a very popular one though in c++, moongoose / civetweb(forked version) are both good alternatives and are test

There are quite a few alternatives, microhttpd is a very popular one though in c++, moongoose / civetweb(forked version) are both good alternatives and are tested in the field and are written in C, you also have duda and libonion doing the same http library but with more functions(restful, websocket,etc)