Thanks for the responses, folks!
Yes, from the perspective of Game Design, Alignment is something that I'm passionate about. Why? Here's how I usually explain it. In Christianity, you have Good (Jesus) vs. Evil (Satan). Think of Heaven and Hell as two different metaphysical planes. Ok? Now, imagine seven more metaphysical planes. At this point, my interlocutors (who are usually non-RPG people) have no idea what I'm saying. So, I draw the Alignment chart on a piece of paper, and I just start to steamroll it. I'm like: Lawful Good, that's the Christian Heaven, Ok? Lawful Evil, that's the Christian Hell. Ok? Well, between Heaven and Hell, there is Mechanus, the place from where the Modrons come from? (confused look from my listener). Look, let's go back to the Christianity metaphor. Angels are from Heaven, and demons are from hell, yes? Ok. Modrons are like angels and devils, but they're not from Heaven and they're not from Hell, they're from Mechanus.
"But how can that be?", I get asked.
Well, because unlike Christianity, which only recognizes Good and Evil, in Dungeons & Dragons there is Neutral. And the Modrons are Lawful Neutral. Heaven, Mechanus, and Hell, are the three Lawful planes. There are also three Neutral planes on the Law/Chaos Axis, and another three Chaotic planes. And all of them are Afterlife Planes.
And there is a place in the Afterlife that is not of this Multiverse: Sigil, the City of Doors, its own pocket-Multiverse, far away from the rest of the D&D Cosmos.