Cumulus is NOT free. If you want to pay nothing, you should get something worth nothing! Cumulus is a very fine piece of software that is classified as Donationware. That means, pay what its worth, and Cumulus is worth a lot! Try Virtual Weather Station FREE for a month, then try Weather Display FREE for a month, then try Cumulus FREE for a month, then pay VWS $100 or pay WD $100, or pay Cumulus what you think its worth relative to VWS or WD.
"What would be the Best FREE weather software?" A package you write yourself!
Just my opinion
George