YAP is a high-performance Prolog compiler developed at
LIACC/Universidade do Porto and at COPPE Sistemas/UFRJ. Its Prolog
engine is based in the WAM (Warren Abstract Machine), with several
optimizations for better performance. YAP follows the Edinburgh
tradition, and is largely compatible with the ISO-Prolog standard and
with Quintus and SICStus Prolog.

Homepage:
http://www.dcc.fc.up.pt/~vsc/Yap/
