In my opinion, the ICO is the blockchain killer app. You don't really need a distributed ledger except in case of digital currencies, which can be used to facilitate transactions in specific apps
There are so many examples, from Canadian Tire Money https://en.wikipedia.org/wiki/Canadian_Tire_money to Microsoft Points https://en.wikipedia.org/wiki/Microsoft_Points showing you can create private currencies granting the bearer certain privileges without a blockchain.