What examples do you have? So far I can think of Steem coin and Dogecoin. The former has the vendor lock-in issue, and the latter has no standardized automation of tipping.
Flattr was probably the most famous. It's still running, last I checked anyway. Readability.com tried something like that as well - remove ads from a site and pay the site owner directly instead. Site owners got very angry about this and it stopped that pretty quickly.
