Is OpenVPN standards-compliant?

As a user-space VPN daemon, OpenVPN is compatible with SSL/TLS, RSA Certificates and X509 PKI, NAT, DHCP, and TUN/TAP virtual devices. OpenVPN is not compatible with IPSec, IKE, PPTP, or L2TP.

Can OpenVPN tunnel over a TCP connection?

Yes, starting with version 1.5.

Can I use a web browser as an OpenVPN client?

No. While OpenVPN uses the SSL/TLS protocol for security, OpenVPN is not a web application proxy. It is an OSI layer 2 or 3 full-mesh internetwork tunneling solution and requires that OpenVPN be installed on both client and server.

OpenVPN runs on:

OpenVPN runs on Linux, Windows XP/Vista/7 and higher, OpenBSD, FreeBSD, NetBSD, Mac OS X, and Solaris.