The Raspberry Pi Zero W has pretty much everything any one would want in the compact size that it comes with, the one drawback is the lack of USB ports. For example, you need at least two USB ports, just, say for a Keyboard and a mouse. This drawback was first overcome by Reference Designer with its Hubpixed that first found its mention in its January 24, 2016 blog. At that time the Raspberry Pi W was not launched and we could have a Wifi on the third USB port and possibly something else on the 4th USB port.
Fast forward, November 21, 2017 and the company launched a new version of the Hubpixed that it calls HubSerialixed. It removes the forth USB Port and adds a USB to UART chip to get you the possibility of adding any UART serial device on this board itself.
Husserialixed is mounted on the back of the Raspberry Pi Zero board. It has four pogo pins that connect to the testpoints +5V, GND, USB D+, and USB D- on the Pi Zero. The Hubserialixed takes power from the Pi Zero board from its +5V and GND ports and that allows it to deliver up to 2A current to the USB ports.
The Hubserialixed has mettalic Hex Standoff pre fastened to it. So all you need to do is to add the 4 provided screw and you are all set. All three ports of Hubserialixed operate at standard USB 2.0 speed (480Mbps). But, if you insert a USB 1.1 device, they’ll all be slowed down to 12Mbps, as it is the limitation of the chipset used in the design.
As for the UART port, it has a nice 4 Pin Header with Power, TX, RX and GND pins. It also has two mounting holes on which you add you own designed board that can fit on the Hubserialixed.
The Hubserialixed is priced competitively on kickstarter. For early backers, it is only $8, while similar competitor products are $10 and over with just the USB ports and no UART.