GNU Prolog is a free implementation (under GPL) of the logic programming language PROLOG. It can compile to native machine code which is extremely fast in execution. Another feature is the included constraint solver.
N.B. THE PROJECT HAS BEEN MOVED TO GITHUB
https://github.com/jiprolog/
JIProlog is a cross-platform pure Java 100% Prolog interpreter that integrates Prolog and Java languages in a very fashinating way.
JIProlog is compliant with the major Prolog interpreters. It supports most of ISO Prolog specifications and the most common and used built-in predicates,
JIProlog allows to call Prolog predicates from Java without dealing with native code (JNI or JNA) and allows to invoke Java...
XGP is an integrated development environment that extends GNU Prolog to work with Cocoa under Macintosh OS X. It provides user interface and graphics facilities largely compatible with MacProlog32 by LPA. Requires Mac OS X version 10.2.1 or greater.