LibreSwan

LibreSwan is an open-source implementation of the Internet Key Exchange (IKE) protocol, which is used to set up secure connections between two or more devices. It is a fork of the original Openswan project, which was created by the National Security Agency (NSA) to provide a free and open-source alternative to proprietary VPN solutions. LibreSwan is designed to be compatible with a wide range of VPN solutions and can be used to create secure connections between different types of devices, including computers, servers, and mobile devices. It supports a variety of authentication methods, including pre-shared keys, certificates, and public key infrastructure (PKI). LibreSwan is widely used in both commercial and open-source projects, and is known for its stability, security, and ease of use. It is available for a variety of operating systems, including Linux, Windows, and macOS. LibreSwan is licensed under the GNU General Public License (GPL), which allows it to be freely used, modified, and distributed.