Sharedcoin is a blockchain.info product. You can read about it on their website, but I don't think it was based on any external design, just a mixing service cooked up by one of their engineers.

Darkcoin and darkwallet also have nothing in common either. Despite co-opting the name, darkcoin's darksend doesn't appear to have anything to do with coinjoin. Their description and illustration in their thread shows some sort of centralized mixing service (more akin to sharedcoin), and indeed their distribution mechanism involves a reward for "masternodes" which perform the mixing with these fresh coins. It would be nice if someone from that project could chime in here and explain just what it is trying to accomplish, because the available technical descriptions are scarce and contradictory.

Darkwallet does indeed implement coinjoin, albeit using a centralized matchmaking service to setup the mixes. I have been informed by the developers that this is a temporary mechanism and they are working towards a fully p2p solution. They do not use the blind signing or ring signature mechanisms which are required to scale to more than 2 participants without revealing ownership of outputs.