From the (super short) Appscope listing:
Metronome, Tuner and Tone Generator
The URL to tap on or type in is musickit.jull.dev/metronome.
Of course, you can turn this into an 'app' yourself with PAWA or just pin it 'as is' on your Start screen. Or just add it as a 'Favourite'. It's up to you. If you're confused by the different PWA options then check out my feature here.
Here's the PWA in action on my IDOL 4 Pro:
A fully working metronome, with audio, and with tap controls to fine tune the tempo (and change the time signature); (right) the tuner, triggering off the phone's microphone (here picking up a very 'sharp' middle C!)
There's a tone generator that didn't actually work on my Alcatel hardware - maybe you'll have more luck on a Lumia? (right) and a Settings/preferences dialog (yes, A4 sometimes needs adjusting if you have older instruments!)