I've built several cross-platforms apps, but never used Appcelerator, the fact that it used C# (Does it still ?)was the main reason behind the fact that I didn't try.

I've used Cordova/Phonegap (where you build webViews, not native apps), which is an OK solution. It's pretty good for rapid prototyping, but the user experience isn't as good as a native app.

>What are the alternatives?

For code reuse & native apps, React native would be a good and modern alternative too.

React native : https://facebook.github.io/react-native/ List of examples apps : https://github.com/maxenceC/open-source-react-native-apps

It's doesn't feel mature yet, but it's a way better solution than webviews.

I've tried some IDE specific for React native, and Deco (https://www.decosoftware.com/) was great !