Thunkable - Powerful but easy to use, drag-and-drop mobile app builder.
Convertify - Convert your website to an iOS and Android app
BuildFire - BuildFire is the easiest way for small businesses to build a mobile app in a matter of minutes for iOS and Android.
Median.co - Median.co (formerly GoNative.io) is the industry leading solution used to build iOS and Android webview apps. Get started for free and turn any website into a full-feature mobile app in seconds.
MIT App Inventor - App Inventor is a cloud-based tool, which means you can create apps for phones or tablets right in your web browser.
appenguin - Turn the most complex web application or website to into an Android app in minutes, for free!