Robinhood - Free stock trading service.
Quantopian - Your algorithmic investing platform
Trigger Finance - IFTTT for the stock market
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.
Senate Stock Watcher - Watch how US senators trade in the stock market
quantra - A public API for quantitative finance made with Quantlib