XCP aka counterparty is an open source "asset/token protocol" that runs on the Bitcoin blockchain by injecting and interpreting additional hash in each block. It allows users to create and exchange tokens with nothing more than a Bitcoin address.

XCP was attempted on dogecoin but "humint" had issues and dropped the project. They had hired one dev and he wasn't inspired much beyond his hourly rate. Pepecoin aka Memetic is the only successful XCP clone running on a POS coin that I know of.  

Bitcoin block times and price volatility can make XCP transactions slow and expensive.

Memetic has built on top of XCP to allow for blockchain based image exchange for trading rare memes.