Pigeon is in private alpha
Pigeon, a private messenger with no phone number, is open by invite on Windows 10, Ubuntu and Linux Mint.
You join with a single-use invite code. There is no phone number to give and no address book to upload. If you want people to find you, you choose a handle.
Your account is a 24-word seed phrase, shown once when you sign up. It is the only way back into the account, and nobody else holds a copy, us included.
Every conversation, one-to-one or a group, is end-to-end encrypted with MLS, the open standard for group messaging (RFC 9420). Groups have no admins: any member can add or remove someone, and everyone sees it. You can link more than one computer, send photos and files, and choose a trusted circle of people to be told if your account ever changes hands.
Messages travel sealed through Pigeon's network of nodes. Each one is stored on several nodes before it counts as sent, and from then on it isn't dropped: if nodes go down, it waits and arrives when they're back.
The alpha is small on purpose. To join, request an invite. The docs cover the rest.