From the Alpha Vantage about page:

Composed of a tight-knit community of researchers, engineers, and business professionals, Alpha Vantage Inc. is a leading provider of free APIs for realtime and historical data on stocks, forex (FX), and digital/crypto currencies. Our success is driven by rigorous research, cutting edge technology, and a disciplined focus on democratizing access to data.

To see more, please visit their website.

To use the API you need to obtain an API key from Alpha Vantage. This is a quick process which is documented on their site.

The API is well documented on their site.

This project is an API client for the Alpha Vantage API written in Java.

If you want to contribute to the project please refer to the wiki for usage and contributing guides.