A 'kibitz' is a silent observer of games, known in board or card games. Scrabble3D has this features too: depending on user settings a game can be kibitzed. You can switch to private mode by clicking the appropriate button at the toolbar. Currently connected kibitzes would be kicked out of the group and wouldn't be able to join again. The same button can be used to switch back to open mode. The last setting is stored on the server.
To observe an open game select the game at the tab game server and chose from the context menu 'kibitz'. Alternatively you might get also invited by one of the player (in this case whether or not the game is public or private). In any case your status will be checked by the server and you become a normal player if you have been part of the game previously. Kibitzes are indicated by an user icon with glasses.
Messages within groups are delivered to kibitzes as well. But it is possible to chat solely with other kibitzes per tattle command respectively the appropriate selection from the receivers list. Kibitzes do not have the right to vote, that means they are not asked whether or not a word is valid or the like. If a new game is started the kibitz remains it's status and will not become a normal player. If you want to be part of the new game you should regroup. But keep in mind that groups are limited to four players.
To end the observation select yourself at the tab game server and chose Leave group from the context menu. If all real players disconnect or leave the group you will be kicked out automatically; a kibitz cannot be an exclusive member of a group.