SWI-Prolog is a comprehensive open source (BSD-2 license) implementation of the Prolog programming language. SWI-Prolog is written in C99 and Prolog and runs on Linux, MacOS, Windows, Android and much more. The system is widely used in education and research as well as commercial applications.

Simplified BSD license
If you use SWI-Prolog and write academic publications, please consider citing one of the papers listed here: https://www.swi-prolog.org/Publications.html
Human-centered Data Analysis

Wielemaker, J. (2019). SWI-Prolog.

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