Also known as GURPS Classic: Voodoo this book took the myths of the mystical religions known as Voudoun and Santeria and gaves them a twist, placing the believers and practitioners of Voodoo in the middle of a cosmic struggle.
It's main feature was it introduced another way to do magic in GURPS totally different from that in Magic, Religion, or Supers.
GURPS Thaumatology adapted its ritual magic system for 4e
GURPS Faerie 109
GURPS Undead 9,14