The WiKID Strong Authentication System is a public-key based two-factor authentication system. It is a flexible, extensible, and secure alternative to tokens, certs and passwords. Application & API support exists for Java, ASP, PHP, Ruby, OpenVPN, TACACS+, etc.
Read our eGuide on how to setup your network with two-factor authentication: http://www.wikidsystems.com/learn-more/two-factor-authentication-white-papers