I made a bare-bones radial (pie?) chart shader, for a mana collection mechanic I'm working on - but then I realised I prefer using vanilla 'resource bars' instead. Hopefully somebody can get some use out of it.
It's using a length from UVs to get a perfect circle for the amounts, but if you swapped it over an alpha step and had an interesting gradient you could get some cool effects as the slice fills up?