There are three of these on the ISS. One connects the Russian modules to the rest. One was used for docking the shuttles. One... kinda just sits there, with modules that were to be berthed canceled. (Edit: PMA-2 and PMA-3 are getting International Docking Adapters (IDA-1 and IDA-3, IDA-2 was lost in the CRS-7 loss of mission) attached for Dragon 2 and CST-100 docking ports.)
Any particular reason for the peculiar shape? One would think having the exits line up semi-concentrically, or having one of the edges line up would be the intuitive approach. So why the heavy slant?