HP Elite x3 is a large screen (5.96-inch) smart-phone. What makes it interesting is the optional "HP Desk Dock" to connect it to a monitor to turn the smart-phone into a desktop computer. There is also a "HP Mobile Extender" to turn the smart-phone into a laptop. There have been attempts at this previously, but the technology, or the users, were not ready. The HP runs Windows 10 Mobile, but Linux can be used in the same way and it can't be too long before Google's Android has a viable desktop option.
It should be noted that there are already generic docking stations for connecting Windows and Android smart phones to external displays and keyboards (you need a phone with MHL socket). Also there is the "NexDoc": a crowd funding project to make a laptop dock for smart phones (essentially a cheap generic laptop with the processor left out and a MHL cable added).