Loops is a federated alternative to TikTok created by Pixelfed. Once it first came out, users were able to sign up for early access. Confirmation emails weren't sent right away, but today they announced that emails were being sent out, and registration is now closed.
I got a confirmation email today, attached in the image. I will be loosely documenting my experience, and may (no promises) make a writeup about it.
I'm not sure popular is the biggest goal right now. It would definitely be nice for federated platforms to gain a bigger user base, but while the tools are growing, it's really inspiring just to think that people are willing to invest the (low or no profit) time and energy into making the internet a nicer place.
Got an invite, too. But without an app there is nothing you can do, just change password and write a bio.