No account or email. You get a random username, stored in a cookie for 30 days so you keep the same name on this browser.
Server keeps the last 25 messages per room in memory for up to 48 hours; it clears on server restart. Regular chats are not written to disk.
Your browser stores style preference, blocked users, unread counts, and up to 50 recent messages per room to restore after reloads. Image files are kept locally as blobs in browser storage rather than inline data URL strings.
Messages and images sent to the "admin" user are saved to disk on the server.
If you enable push notifications, your push subscription is stored on the server to send you alerts.
When using incognito mode, you won't be able to see messages sent to you while being offline.