Speakeasy is a Node.js library for two-factor authentication, providing one-time passcode generation (HOTP/TOTP) with support for Google Authenticator and other compatible apps.
CAILogin (Counter AI Login) is an image-based user verification program for web-page logins. It's written in plain C with no special dependencies, and hence it's very suitable for embedded systems which lack "big" interpreted languages, such as PHP.