Spacebuild (that SVN contains many seperate addons needed for SB3). Spacebuild is basically what it sounds like, the sandbox gamemode, but with added atmospheric conditions, gravity for planetary bodies, and a vacuum in space. Most people run Spacebuild with the Life Support and Resource Distribution addons.
I hope you all give this a try, even if you don't download it for your own game, you should join a spacebuild server at some point in time jut to try it out. Hope you enjoyed this Addon of the Week, I will post another next Sunday.