decreasoner is a Discrete Event Calculus reasoner written by Erik T. Mueller (author of “Commonsense Reasoning“). This is how I build it on OpenBSD 4.7:

• tar zxf ply-3.3.tar.gz
• tar zxf decreasoner.tar.gz
• cd decreasoner/software/relsat-dist/
• tar zxf ../../../relsat_2.02.tar
• gmake -f Makefile.linux
• cp ./relsat ../../solvers/
• cd ../..
• cp ../ply-3.3/ply/lex.py .
• cp ../ply-3.3/ply/yacc.py .
• decreasoner.py executes sort -g. Unfortunatelly, OpenBSD’s sort does not support a -g switch and you have to change it to -n. See also a discussion of sort -g vs sort -n.
• ./make.sh

Someday I think I may contribute a script that may (semi)automate the above…