/usr/local/sbin/openvpn
OpenVPN is a robust and highly flexible VPN daemon. OpenVPN supports SSL/TLS security, ethernet bridging, TCP or UDP tunnel transport through proxies or NAT, support for dynamic IP addresses and DHCP, scalability to hundreds or thousands of users, and portability to most major OS platforms.
/Library/Frameworks/OpenVPN.framework/Versions/Current/bin/openvpn
The binary is a part of OpenVPN public framework.