Softporn is a bit of weird one among the early Sierra adventure games, as it is the only real non-graphical text-adventure Sierra ever published. The game itself was made by Chuck Benton, a field engineer from Boston. It had begun as a programming exercise, but Benton had then got the idea of making some money with the game. This proved to be rather difficult, until Ken Williams, who happened to have purchased a copy from Benton in Applefest 1981, called and asked if On-Line Systems (the predecessor of Sierra) could publish the game. (For a more detailed story, look at the Digital Antiquarian).
Sierra didn’t really change Benton’s game in any way, although there was a talk of a graphical upgrade even back at the day. What they did was design a new game box, with a famous picture showing Roberta Williams with two other lovely ladies in a jacuzzi.