Wire.

Create a local account to use Wire. Your login is stored only in this browser — there's no server, so it won't carry over to other devices.

Sign up

Open this same page in two browser tabs (or two windows), log into different accounts, pick the same room name in both, and you'll be chatting in real time.

Enter room

Runs entirely in your browser via BroadcastChannel — messages sync instantly across tabs of the same browser on this device, no server involved. They won't reach other devices. Attachments are capped at 4MB.