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.
Flora-2 is a powerful knowledge representation and reasoning system designed for building knowledge-intensive applications. It is based on F-logic, HiLog, Transaction Logic, and also supports defeasible reasoning. Applications include intelligent agents, Semantic Web, ontology management, and more.
If you use Flora-2 and like it, please acknowledge it in your project!
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.
A group of systems for building network-oriented intelligent agents, consisting an agent communications infrastructure, April - an agent construction programming language, Go! - a logic programming language and DialoX - an XML-based user interface engine
Mercury is a modern logic/functional programming language. The Mercury system includes a
compiler, debugger, libraries, sample code, profilers, etc. Mercury is designed to be the successor
of logic programming languages such as Prolog.