Two factor authentication is becoming more popular as more and more sites get hacked based on password alone.
- Two Factor Auth - A framework to support a variety of methods as the second factor. The TFA Basic modules provides support for TOTP, recovery codes and SMS via Twilio. These modules are used on drupal.org to provide two factor authentication.
- GA Login uses the Google Authenticator software and smartphone app
- Duo Security integrates the Duo Security tool which includes app, sms, phone callback, and hardware tokens
- Yubikey relies on a hardware device that you plug into your usb port
- Multifactorauth - which requires you to enter a non-evolving pin over your phone to get access. Also has an aim of becoming a bit of a framework module for TFA over Voip.