Swi-prolog is a fast and powerful iso/edinburgh-style prolog compiler with a rich set of built-in predicates. it offers a fast, robust and small environment which enables substantial applications to be developed with it.

swi-prolog additionally offers:

* a powerful module system
* garbage collection
* unicode character set handling
* unbounted integer and rational number arithmetic
* multithreading support
* a powerful c/c++ interface
* gnu readline interface
xpce is an object-oriented symbolic programming environment for user interfaces. although xpce was designed to be language-independent, it has gained popularity most with prolog.