Six Lines of Config FTP Daemon (example config)
This is just my little test project to get started with C++.
Right now it's wrapping SDL2_net (tried asio, but whoa, that's so much bloat there ...). It is multithreaded, valgrind tested and creates a control socket to chat with FileZilla and other clients. It can not list files or do anything useful yet, so you should probably not use it in production right now.