xx Messenger also doesn't require any identification. And unlike Threema:
- it's open source (https://git.xx.network/elixxir/); Android users can build it on their own and load from F-Droid
- it uses blockchain
- no big attachments for time being, but once they come (in 2 months, I hope) they'll be affordable and stored encrypted on IPFS
- no data collection of any kind
- (my guess) better privacy and security
- less polished
- optionally searchable by in-app nick or phone number, or not, in which case you get a cryptographic ID. Identity can be backed up to SFTP and restored from it
Unlike Telegram, xx Messenger app has a publisher, but the app can be installed independently (F-Droid) and there's no centralized entity that runs messaging gateways that can deliver any data about your identity or communications.
Not related to parent comment, but I see some people are bitching about the use of blockchains as if they've figured out a way for Signal or Telegram to provide for their messaging needs without selling ads or metadata.
If funding free messengers was easy and blockchain merely a distraction, Signal wouldn't have those pop-ups that reminder you to donate.