From the developer:

This is a pack which includes (actually) 3 managers: The Config Manager, The Update Manager and the Language Manager.
For Players:
For players it’s just a mod which has to be installed if it’s required. Download for the pack is below.
For Modders:
The config manager gives you the abillity to do the basic thing and make a config for your mods and you can get a free block or item ID. Also modders can make different config files for one mod and also specify a path to their config(s).
The Update Manager let users know when updates for your mods are available. If it’s so, the player gets a chat message when entering a world once, each minecraft session. On servers, it will write into the server log if there’s an update available.
The Language Manager can handle multiple language files for one mod. That means, if your mod is initially written in english, you can use the Language Manager and let it search for language files in the specified path. If it find one, it loads the localizations in there and add them to the equivalent language in Minecraft. Language files must have the language code as file name, for example a language file written in spanish must be named “es_ES.txt”. The file extension can be either txt, lang or SAPLang.

This mod is required for some of the mods on ModMinecraft – only download and install this if the mod you want to use requires it.