So I've only been able to find a single Stars Without Number game on here and its full. I'm currently looking for a GM interested in starting up such a game. I have some familiarity with the rule system, both as a GM and Player. Currently adapting the GM worldbuilding 'minigame' to a fantasy system.
I would suggest that the game be rated at least Mature due to the fact it includes use drugs and mature themes. That being said the choice between Mature/Adult will ultimately be up to the GM.
Here is a free edition of the ruleset. Doesn't include ALL the options but has all the base rules needed to play:
http://rpg.drivethrustuff.com/...-Number-Free-Edition