You could bootstrap initial distribution through an ICO (e.g. if people need an initial stock to be able to distribute it to others). And e.g. in-game currency commonly can be bought, but not sold through official channels.
Re:SEC Shuts Down Munchee ICO
by collinmanderson on Tuesday December 12, 2017 @10:46PM
(#15911857)
Right. The key difference is you're not allowed to sell in-game/app money for USD.
That wouldn't really be an ICO, though, right? You have to be able to convert it back and forth between another currency, not just "earning" it through use of the software to be spent only there and never changing hands.