Mastodon. You can set your own server up and benefit from all othe other existing servers. Mastodon provides a decentralised service running on decentralised infrastructure. You can run your server as you see fit, because access to the wider network is federated.

Zuckbucks provide a centralised service running on decentralised infrastructure. Try add your own server to help run Zuck's blockchain...

Git comes to mind as well, I can go to Bitbucket or Gitlab and upload my repository with its full history in seconds. Or my own self-hosted repository if I wanted.

I don't agree with grandparent for what it's worth, just thought this might work as a reply to your question.

Other than universal entropy, probably nothing. Though math is also decentralized, maybe even moreso, being independent of time. So maybe "nothing that is relevant on a human timescale" is closer.

I strongly suspect that what we have developed a habit of calling decentralization, as if this referred to a final state of a proposed coordination solution, is in fact just a temporary, transitional phase between centralized regimes.