Appium is based on Selenium which is an HTTP protocol by Google designed to automate browsers. The idea is actually very nice as automating an app (especially a webview-based one) is not so different (in terms of required APIs) from automating a browser.
Appium is also designed to encourage a 2-tier architecture: a machine runs the test written in one language (C#, Ruby, JavaScript are only a few among the many supported ones) and another one (the test server) actually executes it. Furthermore the WebDriver protocol targets scalability (because based on HTTP), this makes Appium very scalable as well; remember that you will need to write your test once, Appium will be in charge of executing it on more platforms.