Two Factor Authentication
TFA = Two Factor Auth
OTP = One Time Password
andOTP A fork of FreeOTP that allows you to make encrypted backups. Be careful where you store the backups though!
FreeOTP+ A fork op FreeOTP but with the export of your settings to Google Drive and Android backup. From an opsec pov, if your Google account is compromised, so are you.
FreeOTP Maintained by RedHat, but won't let you back up your keys, unless you use adb. This is a problem because if something happens to your phone (like you want to completely reinstall it) you have a tough time getting your 2FA to work again.
Warning: encrypt your HD if you are going to put the auth system on your PC!
For windows: Winauth
How to set up SSH for TFA
Remember to write down your keys and keep them somewhere safe: losing them means no more access to your system!