It's an ios app. IMO it's really good. I own exactly one apple product, and it's an iPad that only runs Loopy Pro.
Here's a section from the manual that loosely explains the concept[1]:
> Adjust a slider or dial’s value by dragging up and down, or left and right for horizontal sliders. For finer control, move your finger away from the dial.
The only other music or audio app I use with any regularity is Reaper on Windows. I tend to do more performance-oriented stuff, and I try to keep everything outside the computer as much as practical. I don't use any software synths. I like the constraints and UX of dialing patches into my one keyboard/drum machine. I record some, but mainly I like to play in real time and not fiddle with VSTs and plugins.
Here's a section from the manual that loosely explains the concept[1]:
> Adjust a slider or dial’s value by dragging up and down, or left and right for horizontal sliders. For finer control, move your finger away from the dial.
[1]: https://loopypro.com/manual/#sliders-and-dials