Bandcamp docks 15% for revenue share and charges a payment processor fee. Someone recently paid $4.00 for an album I published and Bandcamp gave me $3.15 of it
Assemblage 23 used to do this on their website. It was labeled something like "for anyone who pirated our music and feels bad about it, you can chip in here". But it seems to have been long removed
I guess the closest equivalent is Bandcamp where artists can still use a pay-what-you-want model