The OpenVPN Subversion Repository contains the source code for all versions of OpenVPN.
The root of the repository is here: http://svn.openvpn.net/projects/openvpn
Subversion, an excellent and well documented source code management system, is used to manage the OpenVPN source code.
Check out and build OpenVPN 2.1:
svn co http://svn.openvpn.net/projects/openvpn/branches/BETA21/openvpn cd openvpn autoreconf -i -v ./configure make
View a comprehensive revision history of OpenVPN 2.1:
svn log -v http://svn.openvpn.net/projects/openvpn/branches/BETA21/openvpn