We build planning and scheduling systems in Excel.
Some systems like this material planning example have more than one user, in different locations.
Here is a way to share Excel data across multiple users by using a simple cloud service.
The biggest headache in material planning is long lead-time materials.
Here is a simple tool that gives visibility between a buyer and a factory separated by a lot of water.
Also see an easy trick to connect multiple Excel users on different continents with free data integration over the cloud.
If you do not know your supply constraints, then it is likely your constraint is the MRP system.
How to use constraints-based planning and overcome the limitations of MRP logic.