My wife runs Numenera as a tabletop campaign and has been supporting Monte Cook's games since… hell we've loved him forever. The world is basically Earth but *way* (think, eons) in the future, to the point that it's not recognizable as Earth anymore. Alien species have come and gone, leaving ruins and civilizations in their wake. Nothing is really "explained" fully, they leave a bit of mystery to things, this isn't a game that has any specific set in stone history you must follow; it's full of weird stuff.
"Religion" does exist in the tabletop version because you have multitudes of different races, some alien, some human, some… other… and they all "believe" their own worldview. There are also intelligent androids and such; and some powers (healing, etc) can cause people to gather a cultlike following, but there are nothing like clerics getting powers from "Gods" - though an alien granting you tech might be basically indistinguishable from a "God" in terms of granting power.
I'm actually in the middle of a really creepy printed adventure for the Numenera tabletop game now, I can't wait to play this when it comes out. There is so much they can do with the world and the setting.