Quantopian - Your algorithmic investing platform
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.
quantra - A public API for quantitative finance made with Quantlib
Intrinio - Intrinio is a trading platform, providing professionals with the best in class financial market data API and other tools.
Backtrader - Backtrader is a complete and advanced python framework that is used for backtesting and trading.
QuantRocket - QuantRocket is an all-in-one end-to-end data trading platform and is securing your connection to other trading applications that will be the key to query data and submit orders.