The history of OpenVPN has been bumpy—ranging from a fledgling starter, to widely used, to nearly dead, and back again. The gap in development from 2006 to roughly 2009 was significant, but the hard work and dedication of developers such as David Sommerseth (dazo), Gert Doering (cron2), Steffan Karger, and Samuli Seppänen has given the project a successful recent past and a bright future.
OpenVPN is available on nearly every platform available. Snom (an IP phone manufacturer), for example, includes a version of their VOIP phone firmware with an OpenVPN client included. pfSense, OpenWRT, and other WAP/firewall operating systems include OpenVPN and (usually) a web interface to manage deployment.
In recent years, OpenVPN has been available on many mobile phones as well. The first was available for Android, OpenVPN for Android by Arne Schwabe. This utilized a ported tun driver and did not support tap mode (bridged) VPNs.
The OpenVPN application for iOS (Apple) didn...