This sounds like the "Cap Gripper" --
<http://www.plowhearth.com/product.asp?section_id=0&department=0&search_type= normal&search_value=cap%20gripper&cur_index=&pcode =7369>

It's sometimes recommended for people with arthritis and the like --
<http://www.abledata.com/abledata.cfm?pageid=113583&top=0&productid=74083&t rail=0>

I came across it when I was researching assistive devices before having
shoulder surgery. Check out these jar openers (the wall or
under-cabinet mounted ones are appropriate for one-armed people):
<http://www.sammonspreston.com/Supply/product-list.asp?subsection=518>

--bwg