This inventory drag-drop demo is licensed as public domain.

Try: Drag a selection box to select multiple items at a time. You can drag a bunch of them all at once! If you choose "half", it will split each stack you've selected in half. Shift click to select multiple. You can't select across different inventories by design.

Sample server messages are shown, as an example of what it might look like to notify the server that items have moved.

Create contracts with drag and drop. Perhaps after dropping the items, you could fine tune the quantity and set the location. This is something of a niche use case, and you might need "containers" for that to be really useful.