PlainSight от David Menear

PlainSight is a browser extension designed to allow users to secretly communicate in plain sight. Messages are hidden using a password and are stored within a custom tag as hex. These messages can be placed anywhere on the web and those who have the extension and are using the same password have the ability to read them. If other users are using a different password, the message will become garbled when it is processed and will show up as random characters. This is NOT end to end encryption and should NOT be used to store sensitive data.

For a tutorial on how to use PlainSight, check out the README on GitHub: https://github.com/dmenear/plain-sight