Depends on your definition of "fully", I guess. The only two brewing software I have as comparison are BeerSmith on desktop, and Brewer's Friend. I know that both allow me to enter a percentage for fermentables, as well as weight.
I sometimes see beer recipe grain bills expressed as percentages (for instance, in "Brew Like a Monk", which I recently read), so being new to brewing I assumed that was normal. Is it?