Dave Coffin’s dcraw is the basis of most, non-proprietary, raw converters out there:
https://en.wikipedia.org/wiki/Dcraw
It is open source and converts from pretty much any raw format to start TIFFs. It can do this without applying any modification to the data. I believe that there are Windows versions out there.
A nice application which uses dcraw is rawtran. This converts raw files to pseudo photometric band FITS files: