Those of you who remember my Chzo Mythos series of adventure games may appreciate that I'm coming back to Lovecraftian horror with this one, but this isn't a point-and-click adventure. I like to think of it as a 'Survival Horror Roguelike'.
But there's also a puzzle aspect. One of the four runes of the ritual will be the rune of the god you mean to banish. There are three gods exerting influence upon the world, but only one of those is attempting to invade. If you piece together the ritual but banish the wrong god, then you have failed at the final hurdle. You also need to gather enough clues as to the gods' identities to be able to make, at the very least, an educated guess.
With all that in mind, here's the page with the download link. Let me know how y'all go with it. Bonus points if you record yourself playing for Youtube, 'cos that's as good as a focus test.