I sort of agree with Greek2me. Though, the size of the mod I feel is irrelevant to qualifying as a "system" mod-- I feel that a "system" mod would include, well, a system. Like RTB's add-on, chat, etc system. Simple mods don't add systems, they just add features to the existing systems. If your add-on modifies the main menu, I wouldn't call that a system and would opt for a prefix like "Menu_" or "Client_". If your add-on completely replaces the main menu, then you might be able to consider it a system if it adds enough functionality that makes it not simply a redesign.