Alex Barrotti netted a $45-million exit from Inex, his e-commerce platform, in 1999. Eleven years later, the idea for another start-up sparked in an usual place: a sushi spot in the Caribbean. His friend, the owner, said he wished there was a way to send orders directly from the table to the kitchen. So Barrotti dove into the restaurant business and launched TouchBistro, a tablet app that lets diners order food, and managers monitor the speed and quality of service. The app, which is used in 700-plus Toronto restaurants, handles more than $3 billion in transactions every year.