GAEA (not to be confused with GAIA for Unity), is a newly released terrain generation tool from QuadSpinner. They describe GAEA as:
Gaea takes terrain design toe-to-toe with the rest of the CG landscape. Designed with artists and their vision in mind, Gaea brings together advanced toolsets in an easy-to-use package where you can get Hollywood quality results in minutes.
Using either a simple stack of nodes, or a more complex graph of nodes, you can easily compose primitive landscapes, apply millions of years of erosion and other modifiers, mix and match nodes to your heart’s content, until you get the perfect terrain for your game. The ultimate output from GAEA is height maps that can be used in almost any modern 3D game engine. GAEA is available at a number of different price points, including a completely free but still usable for commercial projects tier.
GAEA is available for download on Windows PCs here. For more details of GAEA, a getting started tutorial, or just to see GAIA in action, watch the video below.