MyServer development has moved to GNU savannah since it became an official GNU Project: https://savannah.gnu.org/projects/myserver
The Vanguard Server Emulator is a free open-source project that will focus on allowing server to client communication using the Vanguard Saga of Heroes client.
NMDC Hub Server
Verlihub is a NMDC hub server that runs on all operating systems. It is written in C++ and has many rich plugins including Lua, Python and Perl.