Killer app would be something which allows you to trade in the exchanges without losing all your coins if they get hacked. That'll bring confidence back to crypto
Are you talking about MGW and uMGW of NXT?:
http://multigateway.com/
All the info:
https://nxtforum.org/nxtservices-releases/how-to-test-multigateway-with-nxtservices-a-test-user-guide/