Two-Factor Authentication, U2F and FIDO2.
The Solo Key comes with:
If you choose the Secure edition of the Solo Key, it comes provisoned, programmed, locked down and ready to use. It is the perfect version for you, your friends and parents. To get started with the Secure edition refer to the quick start guide. This version can only accept signed updates and is protected against readout.
If you choose the Hacker edition of the Solo Key, it also comes provisioned with secure key but it is not locked down and uses a different attestation key than the Secure version. The bootloader of the Hacker edition accepts unsigned firmware. Meaning you will be able to modify all aspects of the key firmware. You will have to lock it yourself to prevent keys being stolen by someone with physical access to the token. You can find the whole software source code of the Solo Key on Github.
For more information about the Solo Security Key refer to the documentation.