Minecraft for the PC is infinitely moddable, being that it's written in Java. The above is a review for a mod that permits the addition of an extra world type that produces glass-bubble "biospheres." There may be some assembly required for PC mods, but the explanation is often availble when downloading.
The Biosphere mod is an addon for Minecraft (compatable with 1.3.2) that adds an extra procedural generated world to the types available in the game. The "biosphere" world type has floating granite spheres with hemispherical glass ceilings each containing its own biome. Rocky spheres also spawn in space between the biospheres, sometimes with mobs on them both hostile and neutral (I've flown over to a few to find chickens and cows.)
As seen in the video, it's possible for a "Nether" Biome to spawn.