Uniswap itself is centralized, using GitHub for centralized repository code storage and the app itself is also centralized. The organization is centralized, with employees reporting into a centralized structure as well.
I suppose there's a spectrum of centralization between "totally controlled by one person" and "magically appears out of the collective intelligence of the entire internet." So I can't say that Uniswap is completely decentralized.
But the code on chain can't be changed by anyone, has no admin functions, and doesn't rely on external data feeds. UI for it can be developed and hosted by anyone or skipped entirely by anyone willing to deal directly with the contract using standard tools. So I'd say Uniswap meets your request above for something that doesn't require a centralized entity. The entities you mention could disappear and Uniswap would keep going.
