ManaCade is a bunch of inventory/GUI based minigames that you will be able to play and compete in global highscores from anywhere on the server.
For now, it will only be available in the Hubs during the beta. Type /arcade or /manacade to access. There will also be a hotbar icon to open it in the Hubs.
Make sure to check it out next time you're waiting for a server to come back online
Progressive games like 2048 will be saved to your profile, so don't worry about losing progress when logging off. If you don't play again for 30 days though, that progress will be reset and your score will be logged.