Check out a node-based procedural and infinite game map generator for Unity called MapMagic by Denis Pahunov.
Each node on a graph represents a terrain or object generator: noise, voronoi, blend, curve, erosion, scatter, forest, etc. Once the nodes are connected the magic happens: a game map will be created without any human involvement.
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No need for painstaking work sculpting and drawing vast terrains, placing thousands of objects, painting fields of grass: just give your orders to the plugin in the form of a node graph and it will create a map automagically!
Denis Pahunov
The tool is said to support multiple biomes: you can blend together forests, deserts, snowy plains, jungle and other terrains.