The OpenL2TP project and its supporting website openl2tp.org are now closed. OpenL2TP files are archived at sourceforge.net.
If you are looking for an alternative solution, ProL2TP may be of interest.
ProL2TP is a scalable L2TP client/server implementation for Linux that supports L2TPv2 and L2TPv3. ProL2TP is designed for network operators, ISPs and network equipment OEMs. Its flexible licensing make it suitable for deployment in small devices or large scale servers. The datapath may be implemented either by the Linux kernel or by an external dataplane, making it a good fit for SDN environments. Source code is available.
If you are looking for an open source L2TP solution, consider the following alternatives: