From the eBay description:
Dates to about 1890, assembled by the firm of August Lasseur, who leased entertainment novelties such as this for public venues. Lasseur would maintain the machines, collect the revenues, etc., in exchange for leasing their space, much the same as is done today with vending machines.
Fitted with a 6-tune Paillard music box, it plays two songs on the drop of a coin. The internal rack of stereoscopic cards allows the viewer to see a 3-D image, which in this case is a naughty picture of a pretty girl. The rack slowly rotates, and another picture soon appears. Each coin drop shows about 4 pictures to the viewer, and when the music ends, so does the show.
Here is the complete listing with many more picture of this Coin-op mechanical musical stereoscope.