"Concept" - How would I go about making a leaderboard save through multiple games?

DataStores and OrderedDataStores can be shared between other places in the same game universe.

If you created a DataStore, and or OrderedDataStore, you can access it in a different place in the same game universe by getting the datastore with the name that was given to it.

Say you've created an OrderdedDataStore with the name 'Ods' in the universe's start place:

local ods = game:GetService('DataStoreService'):GetOrderedDataStore('Ods')

If you wanted to access it in another place in the universe, get it by the same name:

local ourOds = game:GetService('DataStoreService'):GetOrderedDataStore('Ods')

In order to save data in general you would need to use the Roblox Datastores:

http://robloxdev.com/articles/Data-store

The datastores save throughout multiple Places as long as they are all in a singular Universe.

http://robloxdev.com/articles/Multi-Place-Games

Datatores can only save particular types of values inside them which include:

Numbers, Strings, Tables, Booleans, or nil

So in order to save Objects such as a tool, or a Vector such as a position. You would need to come up with a clever system using the available datatypes to store the unusable datatypes in a way that you can load them back up again and determine what they are in Object or Vector form (as an example).

If you need the leaderboard to save through multiple instances of a server (when the player leaves and joins again later), you need to learn about datastores.

Here's a tut on how to save a currency value with a datastore (which might not be what youre looking for): http://robloxdev.com/articles/In-Game-Currency-with-Roblox

there are also videos on youtube that show you how to save leaderboard values but i wont bother linking you to those since theyre easy to find

good luck!