Module script usage?

--ModuleScript (in ReplicatedStorage if you want to use LocalScripts to require it, ServerScriptService otherwise)

local module = {}
module.sharedVar = 27 --Anything inside this table is accessible to things that require() this module.
hiddenValue = 2
function module.getHiddenValue()
    return hiddenValue
end

return module

--(Local)Script

local MOD = require(game.ReplicatedStorage.ModuleScript)

print(MOD.sharedVar) --> 27
print(MOD.getHiddenValue()) --> 2
MOD.sharedVar = 16
print(MOD.hiddenValue) --Errors, since that isn't in the Table.


--A Different script, some time later...
local mud = require(game.ReplicatedStorage.ModuleScript)
print(mud.sharedVar) --> 16, since it was set to 16 in the previous Script.

There is a single caveat to this: Each individual client (including the Server running the game) gets its own copy of the module table.

Modifying it on any of the clients only affects that client, and no others.