Liber XV, The Gnostic Mass
Aleister Crowley wrote The Gnostic Mass — technically called Liber XV or "Book 15" — in 1913 while travelling in Moscow, Russia. He described it as representing "the original and true pre-Christian Christianity." The structure is similar to the Mass of the Eastern Orthodox Church and Roman Catholic Church, communicating the principles of Crowley's Thelema.
Source: Wikipedia — Liber XV, The Gnostic Mass (CC BY-SA 4.0)