This is a keyboard tray using ½" schedule 40 PVC pipe as sliding rails.
“Pipe End” goes on each end of each pipe and allows it to be mounted to the underside of a desk.
“Slider” attaches to the tray and slides along the pipe.
In total you'll need 2 ½" PVC pipes, 2 sliders, and 4 pipe ends.
Design file available here in Onshape.
The author marked this model as their own original creation.