Alt Codes lets you set alternate item codes with special commments, counts, or prices.
Typical uses include:
Barcodes like UPCs can point to your items
Catalog Part Numbers you create and publish can point to your real part numbers
Customer Part Numbers can use their Price, their Unit of Measure, their Margin
Variants or Variations you create in online stores can point to your right part numbers
Vendor Part Numbers can point to your part numbers and appear on PO's