On this topic, I think it is worth mentioning Framasoft [1]
It is a French organization that offers plenty of alternatives to Google and other big tech products. A lot of them are just rebranded and hosted open source software, but they also develop their own, such as PeerTube and Framaprout (the last one is a joke, but PeerTube isn't).
Yup, I'm surprised this wasn't mentioned earlier but they're the ones behind PeerTube (which I see posted on HN a lot) and many other tools. They've been building google alternatives for over two decades now and many of their tools are quite mature
https://degooglisons-internet.org/en/
I hate to say it because it's cute but that website is not going to win over large companies to use these tools.
I don't think they can win over large company, they are just a small nonprofit organization, large companies want to work with other large companies.
Where they can make a difference is for fellow organizations and maybe small companies. A lot of them go to Google because that's the most convenient, even if it sometimes against their principles, they are proposing an alternative.
One minor criticism I have is that while they are not hiding the fact that they are rebranding off-the-shelf free software, they could give them a bit more visibility, should users want to self host at some point.