the index files for astrometry.net are free, but not opensource.
http://trac.astrometry.net/browser/t...ETTING-INDICES
Astrotortilla iteslf runs under windows and uses cygwin to do the astrometry.net platesolves.
http://sourceforge.net/p/astrotortilla/home/Home/
The install guide is worth reading as it gets you past a couple potential sticking points.