Yes it exists, but has been bought by Eyeo. That's the company behind AdBlock Plus, whos' business practices are one of the reasons why so many people have switched to uBlock Origin.
Edit: And it has already started: Eyeo has made major changes to how Flattr works (now they decide who gets your money, and how much of it, not you) and hiked the prices.
I remember when Peter Sunde's Flattr was around (circa 2010) and websites had flattr buttons (like those html/css buttons).
Edit: I just checked and apparently it still exists: https://flattr.com/