Cool! This is the first time I've heard of it, though I'm new to the fediverse. Looks like the project has been super active for years:

https://gitlab.com/soapbox-pub/soapbox

Also, I was pleasantly surprised that you can use https://fe.soapbox.pub/ to try it on your own instance. I don't mind the default Mastadon interface, but the Soapbox one is better (and actually looks a lot like Twitter). Anyways thanks!