App Containers
Application containers were a way of packaging and executing processes on a computer system that isolates applications from the underlying host operating system, using Operating-system level virtualization.
There were implemented using the App Container Specification and Tooling, a project that is no longer active.
Jetpack
Jetpack was a FreeBSD Jail/ZFS based implementation of the Application Container Specification. It uses jails as isolation mechanism, and ZFS for layered storage.
It was presented at BSDCan 2015 (slides, video part 1 / part 2)
Compatibility
Jetpack was developed and tested on FreeBSD 10.x, and compiled with Go 1.4. Earlier FreeBSD releases were not supported.