This is a plugin for the application Rainmeter that allows you to measure the different parts of the Taskbar. This opens up the possibility to get full control over which programs are shown in the taskbar, the notification tray and even control them between different desktops.
This is currently a WIP and it is not adviced to use it in your skins yet as we may change the syntax at any time and will not take any responsibility of broken skins because of this.