XGP 1.1.1 - GNU Prolog development environment. (Free): "XGP is an integrated development environment for GNU Prolog. It extends Prolog with builtins for native Cocoa-based GUI (menus, dialogs) and simple interactive Quartz graphics. Much of the XGP IDE is itself implemented in Prolog.
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MacUpdate - Universal Binary - http://www.macupdate.com/macintel.php