This release represents a merging of the public and non-public versions of Terragen and includes significant new functionality. Some of the highlights are a new rendering method using depth based occlusion culling for greater rendering speed, an enhanced detail mode, new capabilities for the water system and a separate zoom-able terrain preview for more precise editing and camera positioning.

Here an in-depth look at the new capabilites: http://planetside.co.uk/terragen/release09details.shtml