All the cryptocurrencies built on top of techniques that worked on other cryptocurrencies. I really like the iteration speed as well as how non-finite any limitation today is.
For example:
Multisignature transactions are just becoming available. The lack of multisignature made it a non-starter for many applications, including on darknet marketplaces, because rudimentary escrow or deposits were needed. When the operator goes down, all your funds are on their server and are gone with it, but with multisignature as seen in bitcoin and ethereum, you always have control of your funds and they are never in limbo.
Meta-assets are not possible yet. Asset creation is one of the big tenants of Ethereum right now, and there are many assets on bitcoin as well for even longer. Many organizations use this as a way to raise capital, bringing in a lot more capital into the base currency's economies. Monero and crypto note doesn't have this capability yet, but being able to issue and hold balances of these privately, with audit capabilities, will be powerful.
2nd layer scaling solutions are not even on the roadmap yet in any crypto note network. Cryptonote has the same scaling problems as bitcoin or ethereum, but the key sizes accelerate that. Cryptonote coins have dynamic block sizes already, but it may react too slow to really help periods of many transactions. Monero already encounters this issue. Bitcoin style cryptocurrencies have Lightning Network via Segwit. Ethereum has Raiden on the roadmap.
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The same criticisms exist as since Zerocash was just a white paper.
I will say that there is the possibility that they can make the optional opaque transactions the more ready option, but you can look at the blockchain and see that nobody uses those addresses. Zerocash is just a bitcoin clone if you don't use the opaque addresses.
And Zerocash wasn't just a white paper, it was peer reviewed and analyzed by security and cryptography experts.
Not sure what you are trying to say about the papers. I saw they were academic and theoretical.
The academic paper you refer to had both a theoretical construction and an implemented system.