privacyIDEA is described as 'modular authentication server that can be used to enhance the security of your existing applications like local login, VPN, remote access, SSH connections, access to web sites or web portals with two factor authentication'. There are three alternatives to privacyIDEA for a variety of platforms, including Mac, Windows, Android, Blackberry and iPhone. The best alternative is RSA SecurID Software Tokens. It's not free, so if you're looking for a free alternative, you could try stoken.
RSA SecurID Software Tokens: Make strong authentication a convenient part of doing business. Deploy RSA software tokens on mobile devices—smartphones, tablets, and PCs— and transform them into intelligent security tokens.