Alpaca is a Silicon Valley based commission-free API first stock brokerage backed by some of the top investors in the industry globally including Spark Capital, Social Leverage, YCombinator, and Portag3.
Love the idea of Alpaca, but the execution needs work. There is NO SUPPORT, phone or email or chat, and the trade orders sadly often break. I'd rather pay $1 or $2 per trade and have phone customer support to fix my account when there is an Alpaca-caused technical error. Also, I worked with a top developer for months to develop my auto trading algorithm, and webhooks did not work on Mac. It was not profitable.
So far I've been really enjoying Alpaca, been trading with them for a month or so. I recommend it. I just don't give it 5 stars because it takes a couple of days to have the money available for trading when I make a deposit, I use other brokers which make the money available immediately, but besides this I really like it.