I had the idea of making an open world with different biomes to minecraft style but no cubes for exploration and more, but not with that method I can build it. It would be like NoMan’sSky but instead of many worlds would only generate land where it goes by the player with different trees, plants , etc.
You are looking for Voxels. For mesh extraction most likely want to use marching cubes. Here is a nice Nvidia article on how to generate terrain on your gpu.
For a voxel framework I can vouch for PolyVox. It is a free, low level c++ framework and I made this with it. You might want to look into VoxelFarm.
That being said. You are looking at something that is very complicated and needs deep knowledge of c++, math, mutli-threading and other optimizations. There is no Make No Man’s Sky Game - Button in the engine.