[pjc50]

From the translated page:

"Although Japanese is primarily written vertically, there are not many text editors that fully support vertical writing. However, you can gain deeper insight by reading a text vertically or horizontally, or by flexibly changing the layout and rereading it. With Sakishi, you can instantly switch between vertical and horizontal writing while editing a document."

That was my "aha!" moment when reading this. Japanese has been made to fit Western convention a lot of the time, but it's good to have another option.