This is a virtually brand new standing desk converter with dual monitor capacity. We bought it to use at work before changing jobs and no longer need it. The arm attaches to the side of any desk/table allowing you to convert any surface into a standing desk. You can easily convert it back to a sitting desk simply by lowering the arm again. It is an Ergotron Model.
This retails for $530 online.
Below is a description from the website.
A WorkFit height-adjustable workstation moves your keyboard and monitor in one simple motion - change from a sitting to a standing position whenever you want.
This premium stand-up desk solution adds extra ergonomic benefits, allowing the keyboard tray to be positioned below desktop level for optimum computing comfort.
Fold your keyboard up and swing the arm out of the way when you need your desk surface.
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