Some free Skymap resources:
The OTOY skymaps are stereoscopic. At least, I think that’s the term. My favorite is “The Dragon’s Nest”. I couldn’t find a license description but it’s a simple download. If nothing else, download the ones that you like for your personal use!
The ones on the github are ones that I created using Google Streetmaps. Please feel free to use/distribute any or all of them, as far as I’m concerned.