Third-Party Logistics. Essentially the outsourcing of your warehouse/shipping operations to another company.
You should check out NetSuites own Ship Central. It is free if you have the advanced inventory bundle. (Minus the user licenses). I don’t typically recommend it, but it should handle fractional quantities. Big down falls are in order to ship, you must have a packed item fulfillment, and it must be packed through the Ship Central platform.
ShipHawk handles fractional quantities as well.