GNU Prolog is a free Prolog compiler with constraint solving over finite
domains developed by Daniel Diaz.

GNU Prolog accepts Prolog+constraint programs and produces native binaries
(like gcc does from a C source). The obtained executable is then stand-alone.
The size of this executable can be quite small since GNU Prolog can avoid to
link the code of most unused built-in predicates. The performances of GNU
Prolog are very encouraging (comparable to commercial systems). 

Beside the native-code compilation, GNU Prolog offers a classical interactive
interpreter (top-level) with a debugger. 

The Prolog part conforms to the ISO standard for Prolog with many extensions
very useful in practice (global variables, OS interface, sockets,...). 

GNU Prolog also includes an efficient constraint solver over Finite Domains
(FD). This opens contraint logic pogramming to the user combining the power
of constraint programming to the declarativity of logic programming.

WWW: http://gnu-prolog.inria.fr/