A couple months ago, I watched a tutorial video about using Fantasy Grounds's "Core RPG" to build a functional, if clunky, method of doing ANY RPG. I also learned that the rulesets are somehow added to "Core RPG", and I need to figure that part out. There is an online FG "University", which I will join at some point as I'd like to play HARP and other RPGs online.
Roll20 is a nice site, but a dedicated service would be better.