On its 10th anniversary, Signal’s president wants to remind you that the world’s most secure communications platform is a nonprofit. It’s free. It doesn’t track you or serve you ads. It pays its engineers very well. And it’s a go-to app for hundreds of millions of people.
My guess is it heavily private and does not have channels
except that it does. you can make a public group with a shareable link, and change permissions so that only the admins can post.