OpenVPN is an open source, full-featured VPN solution backed by SSL (Secure Sockets Layer) and designed to accommodate a wide range of OpenVPN server functionality, including site-to-site VPNs, remote access, and Wi-Fi security.
It can also be used to implement enterprise-scale remote access solutions with failover, fine-grained access-controls, and load balancing, as well as simplified OpenVPN Connect UI and OpenVPN Client applications for a wide range of operating systems.
Implements both OSI layer 2 and 3 secure network extensions
The project implements both OSI layer 2 and 3 secure network extensions, using the industry standard TLS (Transport Layer Security) and SSL (Secure Sockets Layer) protocols. It is compatible with the GNU/Linux, Mac OS X, Android, iOS, and Microsoft Windows OSes.
OpenVPN is designed to support flexible client authentication methods based on certificates, two-factor authentication, and smart cards. Keep in mind though that it's not a web app proxy and it doesn't operate through a web browser.
In addition, the OpenVPN Access Server is designed to support a plethora of configurations, including granular and secure remote access to internal network services, as well as private cloud network applications and resources, while offering very precise control.
Used by numerous small and medium-sized businesses
Numerous small and medium-sized businesses chose to use the OpenVPN for providing their employees with remote connection support for working from home or abroad.
While the project is actually a daemon service that runs in the background and can be access only via a X11 terminal emulator or the Linux console, a wide range of GUI (Graphical User Interface) front-ends exist for it, allowing end-users to easily connect to a specific OpenVPN server using pre-defined configuration files.
All in all, OpenVPN is a great, open source and free alternative to similar, yet proprietary or hard to implement VPN solutions, such as L2TP (Layer 2 Tunneling Protocol), PPTP (Point-to-Point Tunneling Protocol), and IPsec (Internet Protocol Security).