Twilio Inc. (TWLO)

Verification codes, delivery notifications, a driver calling a customer through a masked number — most of that passes through a platform like this. For a developer it replaces negotiating with carriers in dozens of countries: one call to an interface is enough.

The economics are awkward: a large share of the money received is passed on to carriers, so the figure to watch is gross profit rather than revenue. Billing is by volume, and customer activity translates into results directly. Risks: rising carrier fees, the shift of conversation into messaging apps and competition from platforms built into the clouds. The company pays no dividend but buys back stock.