XPiNC is IBM Lotus Notes XPages in the Notes Client
XPiNC = IBM Lotus Notes XPages in the Notes Client.
XPages is IBM's Java Server Faces (JSF) implementation for Lotus Notes and Domino. In extension to JSF it supports JavaScript as server side language and provides XML driven user interfaces, assembled by a graphical editor and compiled at design time.
XPiNC is these JSF applications running in a Notes client. The client uses the IBM Expeditor framework to provide a web container and XULRunner as HTML rendering engine. In extension to standard browser behavior Notes client awareness is build in. E.g. automatic authentication of the user or ability to open tabs in the client.