Simul CloudWright: a technology for creating stunningly realistic sky images
Editor: Simul CloudWright: a technology for creating stunningly realistic sky images for games and media. CloudWright uses the physics of light to Create high-dynamic range, 360-degree panoramic skies. Save as cubemaps, sky Gradients or individual images. CloudWright is free to try, if you buy a license you can export images.

CloudWright Features
physically correct time-of-day sky coloring
3D volumetric clouds
anisotropic haze and fog
Cumulus, stratus and cumulonimbus Cloud coverage
interactive rendering
HDRI
cloud rendering to .hdr images, .jpeg, transparent .tga and .dds cubemaps
combined or separate sky gradient rendering to .jpeg, .hdr and .tga
real time interactive previews
XML and binary files compatible with the Simul Weather SDK you can free download CloudWright 1.8.0 now.