VSTAR (the Versatile Software for the Transfer of Atmospheric Radiation) is the primary radiative transfer solver that I use. I’ve written an introduction to it below but the formal sources are Bailey & Kedziora-Chudczer 2012 and, more recently, with the transmission and vectorized (polarized) solutions incorporated, Bailey, Kedziora-Chudczer & Bott 2018. Also available through the (password protected) links below is help with setting up and running VSTAR, and a troubleshooting guide being actively edited as new issues are identified.
VSTAR is not currently publicly available, but we would be pleased to work with you if you’d like to get in contact.