SimpleX might be worth a look. Although, I think the developer eventually wants to pursue a two-tiered business model. Otherwise, for something like Matrix (where there are several client apps available), no-one’s forcing you to give over your actual details.

What exactly do you mean with anonymous? Group chats with random, unknown people; or tracking free 1:1?

SimpleX Chat and Briar. Also check this link out.

https://github.com/pluja/awesome-privacy#instant-messaging