One of the most well-known
commercial implementations of the
computer language Prolog, and one of the few that is still
maintained. It is written by the SICS company in
Sweden.
It includes lots of nifty tools, e.g. for integrating Prolog in C and C in Prolog. Also, it includes a wide variety of extensions, so that you have a Prolog that can make TCP/IP connections and so on. It can compile Prolog programs so that they can run without the necessity of a Prolog interpreter.
It is expensive -- and is far more likely to be purchased by a university than by an individual, but SICS has an excellent reputation for support.
More information can be found at its Web page: http://www.sics.se/sicstus/