When you say "free software", do you mean free samplesets (organs), or do you mean non-Hauptwerk VPO software (which we aren't allowed to discuss here on a Hauptwerk-dedicated forum)?
If samplesets, look for the green label "Free" at https://piotrgrabowski.pl/instruments/
There is also a list of free or limited demo samplesets at http://www.pcorgan.com/SampleSetsEN.html
And a monthly subscription to Hauptwerk Lite would let you use 7 for a while at a relatively low cost.