Two years, $16 million and 500,000 eager, waitlisted customers secured Robinhood a place in the iOS App Store as the first, brokerage-fee-free stock trading app. 

While some electronic trading sites — like E*Trade, Fidelity and Schwab — are more affordable than traditional brokers, they still charge fees that range from $7 to $10 per trade and minimum deposits in the hundreds. The Robinhood app doesn't charge any fees per trade or minimum deposits. 

The apps makers advertise that they want to "democratize access to financial markets," but they may just be tapping into a largely ignored market — younger users with a smaller disposable income looking to stretch their dough.