I'm still kinda that Opera Unite didn't take off. It was a decentralized server built into the Opera browser, that was easy enough for regular people to use. You just set it up in a config UI in the browser and could enable features like chat, blogs, photo galleries, a music player, etc. At the time, everyone had UPnP enabled, CGNAT wasn't a thing, and Opera handled UDP hole punching for it, so it mostly just worked. https://www.wired.com/2009/10/opera-unite-puts-the-web-server-in-your-web-browser/

This was back when Opera were still based in Norway, had their own browser engine, and were very innovative. A large number of features that became commonplace were in Opera years before any other browser, like tabbed browsing, full-page zoom (browser zoom used to only increase font size while keeping everything else the same size!), restoring your tabs when you re-open the browser, pop-up blocker, a new tab page that shows your commonly accessed sites, private/incognito browsing, sidebars, and more.

Sure, there's a bunch of downsides to a server being built into your browser, but it was an interesting idea. People that don't know anything about servers were able to easily try it out.