I like role-playing games, but lack the time, energy and (it has to be said) the imagination to come up with interesting plots. I also lack the players - my family will play sometimes, but I'm not sure that we're always looking for the same thing in a game. And I prefer to play rather than run the game - as do they.
So I love tools that will act the role of a GM - providing me with prompts to drive the adventure and the adventure itself, whilst leaving me free to play the character. And, whilst it's not new, I got hold of another one today:
Like any tool, there is almost certainly a knack to using it effectively, but it's more in creatively interpreting small things and building them into a developing plotline and the setting you have chosen for the game, rather than having to have large amounts of plot and characters worked out before hand.
What's nice about this tool is that it has an attached forum to discuss ideas and changes, ask questions and, of course, post example adventures.
A mobile-friendly version is promised. It's things like that make me keen to get an iPad.
Update: In case anyone is wondering how a solo RPG works, or what the point of playing one is*, then there's an excellent post (with some example mechanisms that are no in the tool I linked to) at Tiny Solitary Soldiers.
*Even if you plan to run a game with players, one use is that it gives you a chance to try out the game first, before inflicting it on others.