Quantopian's revenue model is to build a hedge fund and charge the fund investors returns/management fees. The algorithms in the hedge fund come from the Quantopian community. We work with the best algorithm writers on our platform, negotiate compensation, and then put their code to work.

We would be crazy to charge people to use our platform. We need thousands of algorithms, and charging for the platform would be one of the faster ways to kill our business.

Yes, you can code to Interactive Broker's API. But where would you get your free minute historical data for backtesting? Or corporate fundamentals data? Or the free IPython research environment? Or the community of 60,000 quants giving each other mentoring and advice?

I work at Quantopian, so you can imagine my answer to all of those questions.