Well, it's a MUD/MMO rather than a SP RPG, but you could try Gemstone III. (EDIT- oh, guess they're up to IV) Gemstone began its life as a Rolemaster RPG, and when I last played it (a looooong time ...

Another day, and another great pen and paper RPG is being made into a computerized powerhouse. This time around, its Spellbinder, Mythic Entertainment's RPG based on the Rolemaster RPG rules system.