Spacescape is a free tool for creating space skyboxes with stars and nebulas.
Download the latest version from sourceforge.net (Windows/OSX)
Spacescape comes with 3 example files in the “save” directory and 10 billboard star textures in the “media/materials/textures” directory.
You can use Spacescape to make skyboxes for your free or commercial game, no license or royalties required!
Using Spacescape with Unreal Engine 4