P2P alternatives for centralised products

services to replace: Amazon eBay Aliexpress

services to replace: any file hosting
File sharing using WebRTC, ideally for IM which not supported DCC.

Cjdns is a networking protocol and reference implementation, founded on the ideology that networks should be easy to set up, protocols should scale up smoothly, and security should be ubiquitous. .

services to replace: Dropbox Google Drive MEGA Microsoft OneDrive Box MediaFire Yandex.Disk and more
protocols to replace: https://alternativeto.net/software/ftp

protocol to replace: HTTP
this compilated kademilia + bittorrent + git + CDN

a lot of time will pass before he accepts, however, he would solve the problem of the almost all services

https://github.com/ipfs/ipfs

centralised services to replace: YouTube Vimeo Dailymotion Metacafe LiveLeak

Also worth mentioning: PeerTube

Protocols replace: https://alternativeto.net/software/email
email is great protocol which is de facto standard hovewer does exists experiments with p2p version.
Also worth mentioning Jami Ricochet Bit Chat Cryptocat RetroShare

P2P communications have a cons that isn't federated so not recommended every day. one exception is here Riot.im but isn't P2P.

centralised services to replace: Google Search DuckDuckGo Qwant Bing Yandex.Search Gigablast Yahoo! Search ....

Problem is with non-free database. Sure, does exists project like searx which is metasearch in some engines hovewer it's just prosthesis.

centralised services to replace: Facebook Twitter Google Plus VK Gab Tumblr ...
mastodon worked similar to XMPP, is decentralized, fully interoperable, federated using ActivityPub