These days there is RED which comes close to what WCD was but the user base is a fraction of the size and will never reach WCD because torrents are far less popular.
I don't get peoples obsession with only using acronyms when you can just Google "<acronym> tracker" and get the name.
What CD was a private music tracker. It's hard to describe the range of music that was there. And there was a huge community that really knew its music so you could discover some really cool music through collections and the forum.
Redacted is the tracker that rose up as it's replacement after What CD was shut down.
Googling "RED interview" should provide you with an alternate pathway in, however.