I think Flattr comes very close to that. You set a monthly budget and then "flatter" the sites you like. The budget is divided among these sites.
Flattr is a Sweden-based microdonation provider founded by Peter Sunde and Linus Olsson and launched in March 2010.[1]
https://en.wikipedia.org/wiki/Flattr
Also, different countries in Europe solve this problem differently. Some have this system, such as Piano.