One result from Unity’s “Summer of Code” project is now available as Sandor Moldan’s “Terrain Toolkit 1.0”.  From his own description:

Unity already has a powerful terrain engine as one of its core features. The Terrain Toolkit expands on this by providing the user with the ability to rapidly create a variety of different landscapes directly within Unity without needing to use third party software. An additional advantage is that landscapes can now be generated dynamically at runtime. This means a Unity game can have a potentially infinite number of levels or landscapes with a negligible impact on the file size.

Basically it adds procedural terrain generation algorithms and UI tool to Unity, letting you get away from manually modeling & importing terrain in other packages.  A welcome addition to a continually growing product.

via Unity Technologies Blog » Blog Archive » Summer of Code: Terrain Toolkit Released!.