Basebox-Packer
A comprehensive set of Packer definitions. It has quite a collection of 64 bit and 32 bit images for Vagrant VirtualBox and VMWare. A good place to learn Packer definitions.
linux open-source virt shell
Docker
Docker uses LXC to create and manage native, sandboxed virtual containers. LXC containers acts like a separate OSes, can install their own packages without affecting anything else, and overall have almost the same flexibility of VMs but without any of the virtualization overhead! Docker adds a ton of features, like an elegant configuration file that automates many things (like port forwarding, disk/directory mounting, networking, etc), a way to create and share readymade images that can be distributed as appliances, etc.
linux open-source virt cloud-paas provisioning go