I first started roleplaying when Traveller was the new kid on the block. Traveller actually had pretty good support for solo play, and I believe it was a deliberate part of the design.
Most games aren't very good for solo play (and traveller had some pretty big flaws, too) - taking the part of both player and GM, you have to be very disciplined and it's very easy to lose interest. Outside of combat, there are no surprises.
Modern conflict resolution games allow you to come up with interesting ideas for what might happen, and then leave the outcome to the dice, and then play out the consequences. That's pretty good for solo play, but there are still problems. The fact that there are usually no constraints on the GM's power and creativity means that such games are often too 'open' to sustain interest.

But Agon, with its Quests and Strife mechanic, and rule that "nothing can be inflicted on the players without a roll first," and the converse: "players can't achieve anything meaningful without a roll first," (so that you can create plot twists ahead of time, and not be sure if they'll apply in play, for example) all strikes me as creating pretty good synergy for a solo game. I think it's the best game I've seen for solo play.

Has nayone else considered this?