Teddit and Piped don't use any kind of official API to get the content off the respective websites, so they continue to work, even after Reddit's API restrictions that went in place today. It's a different story with Twitter. Interested folks may track the GitHub issue here.
Isn't it just amazing that we've made it to a point where we really don't need big companies to do any of this stuff for us anymore?
When you start to realize it's all very possible for people and communities to just run their own infrastructure, and they don't need to deal with advertising, they don't need to deal with weird ceos, and for the most part the user experience is extremely comparable or even better in some ways, it's almost like that moment that you realize someone was pulling the wool over your eyes. It turns out maybe we didn't need that guy after all.
I’d venture to say we never did need companies to do this stuff. The big companies you think of, Reddit, Facebook, YouTube, all started out as small startups running on a server stack in a basement. The golden age of the Internet was founded on passion projects running on used enterprise hardware. We have always had the capability to run social media sites or video streaming platforms, but as popular sites grew into the companies we know today we centralized and outsourced web management to them. Additionally, as the internet’s userbase expanded to the general public there was a loss of tech-savvy that used to be a prerequisite to being online. Folks don’t need to know a lick of code or even basics of how an operating system works to browse the internet, so naturally these masses think that the internet has somehow always been dominated by a few mega-corporations.
Decentralization, development of FOSS alternatives, and making alternative web platforms is not an evolution for the internet, but rather we are returning to our roots.
The others still work because you can scrape from the website, in particular without being logged in. Twitter just changed to requiring logins.
Reddit will likely follow soon after, given how Steve Huffman's nose is turning gradually more brown, with a musky scent.
YouTube has been gradually shifting this way, but the arms race there has been more pronounced, with plenty of initiatives working at getting around it (eg NewPipe).