They do lots of stuff. A YubiKey 4 has GPG Smartcard, U2F, PIV (SSH,CA, Windows Remote Login), Static Password, Yubikey OTP, Challenge Response Mode (HMAC) and

They do lots of stuff. A YubiKey 4 has GPG Smartcard, U2F, PIV (SSH,CA, Windows Remote Login), Static Password, Yubikey OTP, Challenge Response Mode (HMAC) and HOTP. It does a lot of stuff, I am amazed how cheap they are. Pure U2F sticks can be done much cheaper. The Yubikey one only costs 18$, but the U2F standards was designed for cheap devices. You can get U2F sticks for less then 10$ on amazon.