Well, THIS looks interesting:
In development: GUMSHOE One-2-One, an investigative RPG for one GM and one player. http://t.co/16khYo7G7a
— Pelgrane Press Ltd (@PelgranePress) September 10, 2015
…although I didn’t come to that conclusion until I saw this bit at the main page:
Can’t find an entire game group who can play when you can?
Want an intense head-to-head gaming experience?
Play face to face.
Or take advantage of its superb fit with virtual tabletops to play online.
Bolding mine. Yeah, that sounds like it’d be a handy tool to have. I look forward to seeing the published version.