It's open source and available on Github too. It's made with C# in Xamarin (not forms though, which meansit uses Android's native APIs).
I chose to start with a TOTP generator because
- It's a non trivial use case yet not too complex
- It allows to meaningfully integrate image acquisition and protocol handling
- I already had a UWP version I could reuse the corre logic from
- The Google OTP generator uses a web service to scan QR codes, as far as I can tell
I'd be interested in asking for feedback: does the app's UI feel right? What areas can I improve?