All features that currently exist:
1. All items in the hotbar (configurable number) are sorted left-right in recent use, or right to left if you enable it in mod settings.
1. If there is already an item in the hotbar, it will move to the front and everything slide to fill it's gap
2. If you remove a filter, it will fill the gap instead of moving everything
3. Customisable hotbar that it works in, not just hotbar 1.

It needs to be installed on the server i think, but you can disable it and enable it in the per-player mod settings.