Spaceflight Simulation/Gaming Tools

http://www.spaceengineersgame.com/ Voxel-oriented space construction and survival. Kind of a high-tech/high-rez Minecraft.
http://orbit.medphys.ucl.ac.uk/ Classic, insanely accurate orbital mechanics; many, many historic and SF spacecraft available
https://kerbalspaceprogram.com/en/?page_id=7 Accurate orbital mechanics, not quite as insane
https://www.nomanssky.com/ Updates have brought this originally sparse procedurally-generated exploration-and-survival game to quite respectable levels of playability
http://secondlife.com/ Faded from its 2007 glory days, this complicated social/building VR platform still has extensive Star Wars, Star Trek, Firefly and other SF role playing communities.
https://3dwarehouse.sketchup.com/search.html?backendClass=both&q=space hundreds of 3d-mesh spacecraft models are available here; with skill they can be exported to Blender and other modelling tools