Please check out a list of selected integrated apps here.
TradingView has been one of the most used integrated apps among the users where TradingView users can buy and sell US stocks with commission-free directly from TradingView's web-based charting interface.
Also, please see more examples and how to here.
Commissions Disclosure: No minimums. Commission-Free trading means that there are no commission charges for Alpaca self-directed individual cash brokerage accounts that trade U.S. listed securities through an API. Relevant SEC and FINRA fees may apply.