The Web Authentication Working Group will develop recommendation-track specifications defining an API, as well as signature and attestation formats which provide an asymmetric cryptography-based foundation for authentication of users to Web Applications.
https://github.com/google/OpenSK - OpenSK is an open-source security keys written in Rust
https://github.com/solokeys/solo - Solo: open security key supporting FIDO2 & U2F over USB + NFC
https://github.com/makerdiary/nrf52-u2f - nRF52 FIDO U2F Security Key
U2F USB token optimized for physical security, affordability, and style