Recent - 3DE is interesting map editor that can load and save Quake 1,2,3 map , md3, md2 and more , also bsp version 46 ( Quake III and Enemy Territory ) and bsp version 47 ( Return to Castle Wolfenstein )
Maybe it can be usefull for editing , terrain creating
Here is download page http://sourceforge.net/projects/recent3de/
And here homepage http://recent3de.sourceforge.net/
This software is older - but it is not problem, also source code is included
There are also other interesting editors
Torgue game constructor http://www.garagegames.com/products/constructor
Gile-s - level editor http://www.frecle.net/index.php?show=projects
Unlimited Drop pro http://moraldigames.com/UDropPro.html#
Artifex 3D Terra - 3D terrain editing http://www.artifexterra3d.com/
All free
