While watching some of the videos for RAGE, I noticed they often mention their Megatexture thingy. But im confused if this is actually anything new. There are for instance a bunch of console commands in Doom 3 that are related to megatextures, and I beleive that the game "Crysis" has some kind of megatexturing too, although they call it Texture Atlas instead.

Looking at the Wikipedia page, it states that a more advanced version of Megatexturing is used in Id Tech 5 for Rage and Doom 4 and is called "Virtual Texturing", but isn't there already something with the name of this? Gears of War for Windows and Unreal Tournament 3 in DirectX 10 support something they call "Virtual Texturing" which basically lets the video card use system ram for video ram for textures.

Can anyone clarify this mess? It would be greatly appreciated

I know about as much of as Wikipedia does. All I really know is that with megatexturing it doesn't matter how detailed or complex the texture gets it will never slow down the game. So once the geometry is made it doesn't matter what you paint it with and how High Quality the textures get, the framrate will never suffer.

To get the details you would have to ask Carmack himself. Maybe try emailing him?

P.S. Carmack said that in id Tech 6 he wants to visualize geometry as well. He is a genius.

But I thought it was impossible to animate voxels like Wikipedia says Id Tech 6 will support

Stop breaking the laws of nature haha
The impossible seems to be what Id Software is best at

ID Tech 5 engine was done with the technology "MegaTexture" and "Virtualtexture" for modifying each of the pixels in the world and add any details. And it is time the world is several images are only images 128000x128000 giant pixels and that means not long to load and therefore does not force the CPU and the GPU.

MegaTexture is based basically in a giant superimagen instead of several pictures in the world and so are not loads of textures and therefore does not force the memory.