The computer
The internet
WTF? Calling a computer "decentralized" is like calling a washing machine "decentralized". THat statement makes no sense. Internet is not a "thing" -- it's just a name of a network, and for most people it's not decentralized, as they connect to internet via their ISP, and even most of the traffic on the internet (if not 99.9%) go through centralized servers like google, netflix, amazon. P2P traffic is mostly the file sharing software used by pirates.
Would you consider the printing press a form of decentralization?
The fact that the printing presses might have been controlled by some centralized printing press cabal is not relevant as compared to the ability for printed words to reach the masses. Prior to this I think it was the church and royalty and wealthy who even had access to books.
So as ridiculous as it might sound, the computer and internet are decentralizing
It is all relative. That means even if something is not 100% decentralized, if it is less centralized than previously it is a movement toward decentralization. Even if the websites are controlled by centralized entity. The fact that individuals can publish their own website to the world, this is the printing press to the extreme.
so if the printing press is decentralizing so is the internet and personal computer
James