We’ve open-sourced the most important component of the massive multiplayer server we use for the X-Plane flight simulator: an implementation of the RakNet protocol.
You can find it on GitHub, under the MIT license: https://github.com/X-Plane/elixir-raknet
A bit of background:
RakNet is a popular C++ library for doing game networking. It provides things like stateful connections, client clock synchronization (the bane of every network game programmers’ existence), and both reliable and unreliable UDP transmissions, so you can choose how much latency your packets can handle.
This is pretty niche stuff, but maybe it’ll be useful for someone else. Reverse-engineering this stuff from the RakNet source was, uh, a bit of a pain. 😄