I know that the complicated invitation system is one of the biggest flaws of GameBox. Here comes the first feature to improve it:

• Made the invitation system easier by adding a clickable message that gets send to the invited player. The message will open the GUI which contains the invite.
  • To make that (JSON) message fully configurable was quite some work. There are more then a dozen new messages in the language files!
  • I am not using the classes for ClickEvent/HoverEvent or anything else from the net.md_5.bungee package, thus the plugin is still compatible with Craftbukkit
    
  • The clickable message can be opt out in the configuration file (default is true). Path: "settings.invitations.clickMessage.enabled"
• Up until this version it was possible for players to pick up items while they were in game and the item would show up in the game/GUI. The main problem was, that the item would be deleted as soon as the player closed the game/GUI and his old inventory was restored.
  
  • I did not want to disable picking up of items completely while players are in a GUI or game. With my fix, picking up is still possible, but the item will not show up in the GUI. It will be added to the old inventory and will be restored. If there is no space left in the players inventory, picking up is disabled.
    
  • Fun fact: noone ever told me about this problem and I never experienced it. The idea to test it came to me while I was sleeping (honestly... GameBox is stealing my dreams now).
• Improvements in the default config
  • I doubled the time an invitation is valid for
  • Added two short comments describing the timing options
• Corrected german language file. It's my mother tongue... but my spelling is not perfect

Spoiler: New game coming soon!