Modern smartphones have CPUs that are as powerful as laptop processors of a few years ago while consuming a fraction of the power.
Devices from Samsung, Crosscall and Motorola feature a built in desktop mode that provides supports a second display when connected via a USB-C dock or directly to portable displays over USB-C.
These smartphones can thus provide an alternative to a desktop or laptop computer, when plugged into one of these displays, using the same mobile applications or web applications but on a larger display.
If used with a Virtual Desktop or Cloud PC (a PC running remotely on a server somewhere), then it provides access to Windows applications, just like a Windows PC or laptop!