"HU Prolog" - a portable prolog interpreter from the '80s
HU-Prolog was written by 3 people @ Humboldt-University Berlin (East Germany). See License.txt for more information.
It is written in C, K&R (pre Ansi-C) style.
It did run on a bunch of systems, from 8bit CP/M (or the equivalent versions from eastern Germany from this time), over MS-DOS, multiple 16 and 32 bit Unix dialects and also big-iron platforms like VMS. There where ports to BeOS and Acorn Archimedes
The source code of the core system is available here. Be aware, most comments are in German - because this where the '80s in East Germany.
Some commercial extensions like a dBase interface are lost.
It may or may not compile on todays systems (is still working on current MacOS 10.10, but seems to have issues on the travis-ci 64bit Ubuntu platform.
In the last ~30 years (~1987 and 2016), the performance increased by a factor of 2^14 - just by recompiling the programm on a modern MacBook instead of a Z8000 16bit Machine.