As I recall, there were a total of five "solo" adventures actually published "officially." They were, in no particular order:
Alone Against the Dark (Chaosium)
Alone Against the Wendigo (Chaosium)
Grimrock Isle (Triad Entertainment)
Alone on Halloween (Pagan Publishing)
and, most recently, Alone Against the Flames (Chaosium)
Of the three I've played, I always considered Grimrock Isle the "toughest;" I lost more player characters in that adventure... Fortunately it was set up so that your new character could pick up the threads in a "in-game" way that didn't disrupt the play. It actually played like an HPL novella -- layers of the onion, and all that. It's also the largest of the five. Of the others, I haven't yet played Alone Against the Flames, or Alone on Halloween, but the original two were excellent and a lot of fun. And, of course, Grimrock was superb.
I don't believe there were any more published solos out there; but I do remember hearing that there were one or two others that were never published -- it was back in the mid- to late-'80's when Fighting Fantasy and other programmed adventures were hitting big...
All of them should be fairly easy to convert to 7th Ed; frankly, 7th Edition is cleverly enough designed that converting or back-converting (if you prefer an earlier edition) is not very difficult.
Edited by jlynn, 08 December 2017 - 10:36 PM.