This is a Trammel of Archimedes ( http://en.wikipedia.org/wiki/Trammel_of_Archimedes ), drawn from scratch after seeing another printed version, presumably Thing 5103.
Drawn from scratch as an exercise in Alibre, where the '2' designates this is really v2 with filleted corners to make it easier to hold and where the elliptical path just barely misses the guide.
When printing raftless with ABS, if you have it too close to the platform the bottom layer might be flattened to too big to fit into the slot and you'll need to perform surgery to cut it off. The model can be improved to account for this but these are the original STL's I printed.
Motion is very smooth if printed with PLA - see http://www.youtube.com/watch?v=rSmlT-N9rQM
Edit : Updated the slider with a chamfer on the base for raftless prints which I often do.
1)Print (The settings I used for Up! are 0.2mm layers, 'fine' and solid/loose fill)
2)Slot the sliders in
3)Put the arm onto the sliders
4)Play during a long meeting
The sliders have a 2.4 hole, where you can tap your own M3 thread and attached a thumbscrew on top to hold the arm in. I found that this wasn't necessary with the black ABS and clear PLA versions I printed using the Up!.
Edit : You don't actually need to tap it!!! Just screw in your M3 threaded screw in! Most PC screws are M3, I used gold thumbscrews :)