Robinhood - Free stock trading service.
Quantopian - Your algorithmic investing platform
Rally Rd. - Invest in blue-chip classic cars like stocks
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.
Freetrade - Invest in stocks & ETFs for free, get started in seconds.
quantra - A public API for quantitative finance made with Quantlib