Co-creator of GURPS Magic (First Edition) and main author of GURPS Grimoire.
Besides the Linked Items below, I have "supplementary material" credit for GURPS Camelot, GURPS Celtic Myth, GURPS Egypt, GURPS Japan (Second Edition), and GURPS Time Travel, and "playtest/commentary" credit for GURPS Arabian Nights, GURPS Aztecs, GURPS Callahan's Crosstime Saloon, GURPS Fantasy Bestiary, GURPS Fantasy Folk, GURPS Imperial Rome, GURPS Magic Items 2, GURPS Middle Ages 1, and GURPS Religion.
More recently, I proofread/edited the English translation of Contact: Das taktische UFO-Rollenspiel (not published yet?) and the English translation of Space: 1889 (Ubiquity edition) starting with the Venus Sourcebook. I was also heavily involved in the final development of Invasions: Volume 1 – 350-650 AD.