So I have a previous post about soloing useing ML20 here and in my research I have discovered a interesting and valid game system I think is worth a try, Flabled Lands. All you need is any one of the books, a pencil, and 2d6.
The books in this system work independently and in conjunction, for less than $30 all three books can be purchased or $8 each. And the game is fun easy and immersive, a near perfect model of what game play should be for solo rpg. I say near perfect because I felt there where situations that I was railroaded into or out of and I would have like to have seen more skill checks. I highly recommend it, I've nearly completed one book and will order another soon.
Please let me know if you have any solo suggestions or ideas!
Here are the links: