In the interests of privacy I suggest using SoftEther VPN as a free alternative to most VPNs. It is a open source multi-protocol VPN software developed by the University of Tsukuba. It is an good alternative to OpenVPN and Microsoft's VPN servers. Since it has a clone-function of OpenVPN Server, you can integrate from OpenVPN to SoftEther VPN smoothly. Incidentally it is also faster than OpenVPN. SoftEther VPN also supports Microsoft SSTP VPN for Windows Vista/7/8.
Features:
•SSL-VPN Tunneling on HTTPS to pass through NATs and firewalls.
•Embedded dynamic-DNS and NAT-traversal so that no static nor fixed IP address is required.
•SSL-VPN (HTTPS) and 6 major VPN protocols (OpenVPN, IPsec, L2TP, MS-SSTP, L2TPv3 and EtherIP) are all supported as VPN tunneling underlay protocols.
•No memory leaks. High quality stable codes, intended for long-term runs.
•Source IP address control list function.
It runs on Windows, Linux, Mac, FreeBSD and Solaris. However, the Linux version of VPN Client has numerous limitations, and currently it cannot be operated using a GUI. Therefore, the Linux version of VPN Client is recommended for use only by users with a very strong understanding of the Linux operating system and networks.
Source code:
https://github.com/SoftEtherVPN/SoftEtherVPN/Forum:
http://www.vpnusers.com/Download:
http://www.softether-download.com/en.aspx?product=softether