I have never used this service so don't consider this an endorsement, however Alpha Vantage seems to fit your requirements (other than being open source, which

I have never used this service so don't consider this an endorsement, however Alpha Vantage seems to fit your requirements (other than being open source, which I don't particularly understand anyways). http://www.alphavantage.co http://www.alphavantage.co Their site says: We have one shared aspiration: democratizing access to institution-grade financial analytics. Alpha Vantage is one of our deliverables towards this purpose. It provides free JSON APIs for stock market data, augmented by a comprehensive set of technical indicators.