Which brokerage is good for international traders and has a dependable API for third party devs?

We are looking to add support for another brokerage to the Optionsmith trading platform because we currently support Schwab accounts only -- and have many folks who want to use the platform but they are in countries where Schwab isn't available. If you are a trader in one of these countries, which brokerage is preferred?

Note: IBKR's API is not viable for this.