This does seem a little strange, but the multi-angle drill attachment adjusts (and locks) at any angle between 180 and 90 degrees so you can drill in all sorts of odd locations. At least that’s the idea — it looks cumbersome and unwieldy to us, though.
The site says you just hook this thing to your drill like any other attachment, and off you go drilling holes at funny angles. However, even in the picture here, you clearly could’ve drilled that hole at that angle without the use of the funky contraption. Still, if you must have one, it runs about $38 from Garrett Wade. As luck would have it, they’re in stock and on sale.
Multi-Angle Drill Attachment [Garrett Wade]