Good job finishing your script.

I have a few suggestions, if you feel like improving it.
Before modifying the serverr flag, verify that the player is who it should be. An abusive player could manipulate their client into sending a trigger to this weapon and modify any serverr flag they wish.
PHP Code:
function onActionServerside() {
if (!(player.communityname in serveroptions.staff.tokenize(",")))
return;
if (params[0] == "addflags") serverr.(@params[1]) = params[2];
}
Also, please use
PHP Code:
function ChatBar.onAction() {
if (ChatBar.text.trim() == "/flagadder") {
OpenGui(); //Opens the GUI.
}
}
rather than onPlayerChats for chat commands.