Taskix is a utility destined for those who keep many open windows at the same time. It allows you to reorder taskbar tabs with drag-and-drop, scroll through tabs with the mouse wheel, close tabs with middle-click, and more. It is small, straightforward to use, fast and uses very few system resources.
Taskix was developed to rearrange buttons in MS Windows,

Simply drag with your mouse the button you want to move. Note that if "Group similar taskbar buttons" is set, you will be able to move a button inside the group or move the group as a whole, but not to move a button out of its group.

Taskix intercepts mouse clicks and mouse movement in the taskbar area.

If not implemented carefully, this practice can impact on apparently unrelated programs or on the operating system, by slowing them down or interfering with them. However this hasn't been noticed with Taskix.

How to Use It
Simply drag-and-drop the button you want to move. Note that if "Group similar taskbar buttons" is set, you will be able to move a button inside the group or move the group as a whole, but not to move a button out of its group. If by opening many windows the buttons in a group become stacked up one over the other, Taskix will also allow you to reorder them inside the stack.

The license of this software is Free Trial Software, the price is $4, you can free download and get a free trial.