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Well that is quite impressive. Is there any other method of doing anonymous transactions currently? (Whether its a service on top of bitcoin or another cryptocoin which implements an anonymous feature)
Also, why is it a seperate action in the protocol and not a standard (all transactions anonymous).
Yes Monero,
https://getmonero.org/home, uses ring signatures to mix with existing prior transactions on the blockchain. There is no need for a separate action for mixing (Coinjoin, or a mixing server), or to wait for a period of time until mixing is completed before sending mixed funds since mixing is built right into the Monero protocol. When one sends Monero mixing is built right into the send funds transaction.
Edit: In Monero anonymity is
not optional, since there is a minimum mixing level required for each transaction, currently 2 and scheduled to increase to 4. The only exceptions are certain dust clearing transactions and coinbase (generation of new coins) transactions.
I don't think it's completely correct to say that anonymity is not optional for Monero, since you could publish your view key and allow anyone to audit your txs, right?