Robinhood - Free stock trading service.
Quantopian - Your algorithmic investing platform
Sumday - Investing how you least expect it
QuantConnect - QuantConnect provides a free algorithm backtesting tool and financial data so engineers can design algorithmic trading strategies. We are democratizing algorithm trading technology to empower investors.
SharesInside - Makes investing easy
CloudQuant - Crowd based algorithmic trading development and backtesing for stock market trading.