Hanger steaks (aka hanging tenders, butcher’s steaks, "thick skirts", onglets) are cut from the plate, between the brisket & the flank. With a slightly chewy, stringy texture similar to skirt steaks, hanger steaks offer particularly full beefy, liver-y, almost game-meat-esque flavor.  Like skirt steaks, they work particularly well with marinades.
 
Until recently hanger steaks were relatively unknown in the US - many American butchers kept them for themselves.  They’ve long been popular in Europe and are considered a classic French bistro cut.  Today they’re showing up on more and more restaurant menus as American chefs discover their beefy flavor and affordable price.