The SWI-Prolog HTTP library is in active use in a large number of projects. It is considered one of the SWI-Prolog core libraries that is actively maintained and regularly extended with new features. This is particularly true for the multi-threaded server. The inetd based server may be applicable for infrequent requests where the startup time is less relevant. The XPCE based server is considered obsolete.
This library is by no means complete and you are free to extend it.