Robinhood - Free stock trading service.
TradeStation - Whether you trade stocks, ETFs, options or futures, TradeStation’s award-winning tools and...
Alpaca Trading API - Simple REST API for commission-free stock trading
OptionsHouse - OptionsHouse is an online stock trading platform with an easy-to-use interface.
Alpaca Data API - Free real-time stock market data API
Merrill Edge - Merrill Edge is a brokerage platform that helps in investing, provides advisory consultations, and other services.