here is a free action set for adobe photoshop
The Domemaster Photoshop Actions Pack is a collection of custom Adobe Photoshop actions that were designed to speed up the fulldome content creation workflow.
The actions provide tools for converting images from several common panoramic formats such as angular fisheye, equirectangular, and cube map panoramas, and general utilities for VR and fulldome production.
converts cube maps
http://www.andrewhazelden.com/blog/2012/11/domemaster-photoshop-actions-pack/
not free but very useful with space engine
(for after effects)
mettle skybox
just bought out by adobe
https://www.mettle.com/product/mettle-skybox-suite/