Short answers

Not in a Secret Chat. Those are end-to-end encrypted, so only the two phones in the chat can read them, and the server deletes its scrambled copy once the other phone has it.

Normal chats are different. They travel between your phone and our server over an encrypted connection (HTTPS), so your network and anyone along the route cannot read them, but they are stored on a single server in Germany in a form that server can read, until they are deleted. When the app is closed, their notification goes through Google's push service with the sender's name and a short preview. The server is administered by one person, and messages are never used for advertising, sold or shared. The security page has the details.

A one-to-one chat that is end-to-end encrypted. Start one from the new-chat button and choose “New secret chat”; both of you need Blackbird 5.3.0 or newer. It lives only on the two phones it was started and accepted on, so it does not open on your other devices and is gone if you lose the phone, sign out or uninstall. Its notifications say only “New secret message”. You can verify each other with a security code, and set messages to disappear.

It is used only to run the service. It is never sold, profiled, shared with a data broker, or used to train anything. The privacy page lists exactly what is stored.

Blackbird is run independently by one person, on one rented server, with no company or investors behind it.

The service would stop with it. Blackbird is free and offered without a guarantee of availability, so keep your own copy of anything important, such as photos and documents.

Blackbird checks on launch, shows what changed, verifies the download against the server's fingerprint, and installs it.

Sign in the way you signed up — email and a one-time code. Add a password later from Settings → Account, or an email to a username account the same way.

No. It is optional, only matches numbers already on your phone against existing accounts, and keeps nothing that does not match.

From inside the app. Your messages go with it. A copy can survive briefly in a backup before that backup rotates out.

Blackbird is coming to Google Play soon. Until then, it is installed directly from this website, and every update is signed and checked before it installs. See the install page.

No. Blackbird is available for Android only, and an iPhone version is not in development.