Serial ports are still ubiquitous in embedded electronics. Crack open any non-trivial device and you will probably find a serial port, sometimes along with JTAG or SWD, on an unpopulated connector or on test pads, spitting out debug logs.

And it makes sense from an engineering standpoint. Equipment for interfacing to a serial port, even in 2022, is widely available (you can get a basic TTL-level dongle for the price of a coffee) and pretty much every microcontroller/SoC has at least one hardware UART. If you want to see what your code prints to stdout while it's running on real hardware you could either implement a fancy redirection layer that sends logs over whatever interface your device has (and hope there are no bugs in it) or just use the built-in UART, wire it up to an off-the-shelf dongle and call it a day.

UARTs are super important still, nothing old or obsolete about that tech. It's simply still useful, and a sensible way of doing serial communication in a simple way.

The Pirate is awesome, and was rather magical when it first appeared (I bought mine in 2010), but nowadays I would just use a USB/UART adapter [1]. They're cheap as ... something cheap on Amazon, and simpler since they're special-purpose.

[1]: https://www.amazon.com/s?k=usb+uart&crid=1JQRTOTBVDDCW&spref...

Wide spread. Its very easy to work with. UART aka Serial TTL or just RX/TX is native to almost all chips. There is no standard protocol though, so unless its a modem (AT commands) or you have a manual you will likely have a hard time communicating with it. If you want to see what is going over the wire get a logic analyzer. Typically ~$30. Connects to USB and comes with software to decode the messages. Its read only so to speak.

Quite common. I will see if I can find a link and or some quick examples.