CardinalDirector is a custom Minecraft layer 7 proxy using code from Bungeecord, Waterfall, Travertine, and Velocity.
It is most notable for its extensive features and configuration, similar to Velocity-CTD, and its security features that build upon EastEngine's, especially antibot and offline login protection.
CardinalDirector is also highly performant; it can handle thousands upon thousands of players on one instance given the proper hardware and networking.
However, if that's not enough, a built-in cross-proxy synchronization system is currently in testing. It will eventually be combined with EastEngine for "multipaper" or regular minigame network type setups as well.
CardinalDirector currently supports clients from 1.7.x through 26.2 and supports any kind of Minecraft server implementation, even modded or vanilla Notchian servers.
CardinalDirector is proudly ran on a handful of various networks, some being SMPs and some being minigame servers.
As of writing, CardinalDirector is only available to a small group of people and will likely remain that way for the foreseeable future.
Also see the EastEngine Minecraft server implementation