I jusrt saw this mentioned in the Swords & Wizardry forum:

X-plorers is a “what if?” game. In this case, what if the fathers of the role playing hobby were more into science fiction than fantasy when they wrote that first set of official rules back in 1974? What if that game was about humans expanding and exploring their universe, instead of delving into deep dungeons to kill monsters to earn treasure? These are the questions X-plorers attempts to answer. X-plorers takes the original fantasy role playing game as a starting point, and morphs it into something suitable for science fiction. Get in on the playtesting of this old school sci-fi game!

You can get a free pdf copy of the current playtest rules here. When completed, X-plorers will have both a free PDF version and a print version. From a very quick glance, this looks interesting. The only thing I immediately dislike is nothing in the document is open game content.