YubiKey - The YubiKey is a one-time password device for secure login with two-factor authentication
Authy - Best rated Two-Factor Authentication smartphone app for consumers, simplest 2fa Rest API for developers and a strong authentication platform for the enterprise.
Nitrokey - Email Encryption. Encrypt your emails with GnuPG, OpenPGP, S/MIME or your favourite email client.
Rublon - Rublon enables your workforce to securely access your organization's networks, servers and applications via easy-to-use multi-factor authentication. Protect cloud apps, VPNs, servers, workstations, internal as well as on-premise apps.
Google Authenticator - Google Authenticator is a multifactor app for mobile devices.
inWebo - inWebo is a SaaS provider of Identity Protection & two-factor Authentication built to secure access to VPN, web sites, Mobile and Cloud Apps.