A Theremin app built using JavaScript and HTML.
This app uses mouse and touch inputs to control a musical oscillator that changes the frequency and volume of the note you hear based on the position you are pointing to.
The x axis controls volume, starting with 0% on the left side and reaching 100% on the right side.
The y axis controls frequence, starting with 0hz at the bottom and reaching 1000hz at the top.
This is an example of an HTML web app that can be added to your home screen and used fullscreen.
Due to design decisions at Apple, iOS users will have to add this app to their homescreen and launch it as an app before mobile safari will allow the user to hear sound from the app.