Water or Blood
The Hands of Old Geth
Sanctioned Ancestor Worship of the Gethenomie peoples, some darker branches exist revering necromancy and darker arts, but these are unsanctioned by the Empire.
Technically The Ancient of Geth the cities great lord is the head of this religion, but it is such a fractured personal religion that this organization is historical and not really how it works. Instead having small cult like groups that revere certain lines of ancestors for great past deeds, and the advice that those spirits offer their still living kin.