Alpaca Trading API - Simple REST API for commission-free stock trading
Robinhood - Free stock trading service.
Matador - Free investing + Social feed of trades + 2.5% on your cash
Alpaca Data API - Free real-time stock market data API
Qooore - Investing app for hypebeasts
Alpaca Fractional Trading API - Commission-free API to trade & invest for as little as $1