How active is Appium?

Appium is available on GITHUB and there you can find all you need. The Appium team is responsible for developing many different subsystems revolving around Appium (like APIs for different languages), thus I can tell you that this product is alive and very active. The team is also pretty well responsive and once you open an issue you will find a reply after no more than 36 hours (this ETA comes by my personal experience). The community around Appium is also pretty large and growing every month.