A self-destructing message is one that is deleted after it has been read, or after a set time. The idea is simple, but "self-destructing" can mean very different things depending on how the tool is built.
WhatsApp, Signal and Telegram secret chats can delete messages after a timer. The message is removed from the conversation on both devices. This is built for ongoing conversations between people who both use the app. It doesn't help when the other person is on a different platform, or when you need to send something once to someone who has no account.
You write the message on a web page and get a link. The person opens the link, reads the message, and it is deleted from the server. The link can be sent through any channel, such as email, SMS or any chat app, because the message itself lives on the web page, not in the chat. That makes one-time links useful for passwords, API keys, recovery codes and other single-use secrets.
For a one-time link, the useful version of this is: the message is encrypted in your browser before it leaves, and the service never has the key. A common way to do that is to put the key in the part of the URL after the #, which browsers don't send to servers. The server stores only encrypted data. When the link is opened, the recipient's browser uses the key from the link to decrypt it.
Encoder works this way, using AES-256-GCM. The stored data is deleted at the first open, or when the timer runs out, whichever comes first.
Try a one-time link. Write a message, get a link, and it is gone after one read. Optional extra password, expiry timer, photo and voice messages. Receiving is free, with a few free sends to try, then a one-time $19.99 license.
Open Encoder