Libreswan - Definition from the Hotspot Shield Glossary
Libreswan continues on from FreeS/WAN and is an implementation of VPN protocol based on IPsec (Internet Protocol Security) and IKE (Internet Key Exchange).
Libreswan has been developed for 15+ years and can be run on Linux, FreeBSD and Apple OS. In the early stages of this area of development, FreeS/WAN saw restrictions in its development due to limitations the owner impeded surrounding code and what could be added into the software. To combat this Free/SWAN was stopped, and Open Swan was developed instead to add new features and allow it to be viable to a greater audience. However after some time, the founders of Open Swan had a dispute over ownership which ended up in a lawsuit and saw the creation of Libreswan.