Religions

Greyhawk Pantheon

This group of gods is worshiped in The Nation of Foran.

Olympian Pantheon

Half-orcs tend to worship the Olympian Pantheon. However, they are extremely transactional in their worship. "I will sacrifice a cow to Poseidon for a safe voyage, and if anything goes wrong, I won't ever sacrifice to him again". Because of this, half-orcs will also petition foreign gods if their own fail them.

Gruumsh and his Pantheon

The Orcs of Haldreth abandoned their gods after the High Elf Cataclysm. They severed their connection to the Orcish god, and within a generation, they were all half-orcs. They kept this moniker to remind them of what they did not want to become again.
Now, followers of Gruumsh undergo a ritual to mutilate themselves. Whatever species they were prior to the ritual, they become Orcs afterwards. Orcs will then take prisoners in their raids, and torture them until they are willing to undergo the ritual. Gruumsh is desperate for new followers, but so far, there has not been an orcish band of over 200 in the last two thousand years.

Lolth

When the High Elves made their deal with Mephistopheles, he agreed to kill every follower of Lolth on Haldreth.  The Drow that survived had already forsaken the Spider Queen.
The current worshipers of Lolth in Haldreth are secret cults, as her name is still hated across the world.  Drow are exceptionally rare in these cults, and most of their activities are to punish the Drow for their betrayal.  Lolth is greatly amused that she has more High Elf followers than drow.
She has also embraced her role as an ultimate evil figure, and will sometimes answer unsolicited prayers.  In Foran, the most common version of this is known as The Curse of the Spider Queen 

Elven Pantheon

The Elven pantheon no longer answers prayers

Druidism

This is the main religion of wood elves