NetVirt <http://netvirt.org>
NetVirt is an open source network virtualization platform (NVP). Our goal is to implement a secure and scalable production quality NVP.
NetVirt is well suited to create a Network as a service (NaaS) that provides multi-tenant L2 network.
Cloud networks are similar to a virtual private network (VPN) because they enable users to securely access files, printers, applications, etc. from anywhere in the world, on any device. However, cloud networks are multi-tenant private virtual cloud networks that overlay the Internet. Each virtual cloud network functions like a borderless LAN and provides fully switched, any-to-any connectivity between servers, PCs, and mobile devices from anywhere. -- https://en.wikipedia.org/wiki/Cloud-based_networking