strongSwan
strongSwan is an Open Source IPsec-based VPN solution for Linux and other UNIX based operating systems implementing both the IKEv1 and IKEv2 key exchange protocols.
ibreswan is a free software implementation of the most widely supported and standarized VPN protocol based on ("IPsec") and the Internet Key Exchange...
ibreswan is a free software implementation of the most widely supported and standarized vpn protocol based on ("ipsec") and the internet key exchange ("ike"). these standards are produced and maintained by the internet engineering task force ("ietf").
libreswan has been under active development for over 15 years, going back to the frees/wan project founded in 1997 by john gilmore and hugh daniel. for more information, see the project's history. libreswan supports ike versions 1 and 2. it runs on linux 2.4 to 4.x, freebsd and apple osx. on linux, it can use the builtin ipsec stack ("xfrm/netkey") or its own ipsec stack ("klips"). it uses the nss crypto library. see the supported features.