I've used one of these before. They are useful for attaching serial devices to an Ethernet network. It's a lot cheaper and easier than trying to put a PC with enough serial ports near every device you need to talk to. The ones I worked with were part of a radio modem sold by MaxStream, now part of Digi International.

I use microcontrollers for prototyping and proof-of-concept work. Often I combine multiple devices into a system that I can control from a PC. It's been my experience that dropping in a something-to-serial converter is 100x easier than trying to install and understand a communication protocol "stack," even if the code and documentation is supplied by the chip vendor.

I tend to use little USB-to-serial breakout boards, but I'd do the same with RJ45 if I needed that interface.

Once something of mine is ready to commercialize, it gets handed over to professional developers who tend to prefer the built-in firmware based approach, but they end up spending a lot of time debugging those interfaces.

RIPE used these for the v1&2 versions of their Atlas measurement network. I've had a few running for about 3 years.

https://atlas.ripe.net/

We use them to add ethernet and new comm protocols to regulated legacy embedded devices that only have serial ports.

Robotics, consolidate all your sensors and controllers onto Ethernet. Its quite hard finding a microcontroller with good Ethernet.

I immediately imagined adding web UIs, or simply network APIs, to various "dumb" hardware. Attach it to a ADC/DAC and suddenly a lot of things become computer controllable. It's small enough to stick it on most electronic device boards without major changes.

Yeah these sort of "look at how small this fully functional computer is" pieces always make me wonder if they have a real world appeal or if they're more a proof-of-concept or tech demo to pull people's attention to the company's other products.

this would be fantastic for corporate espionage, snap one into an unused to drop somewhere and you have a beachhead inside the network. Combine it with a Micro SD card you have a great way to exfiltrate data via weekly/monthly data drops, without setting off external firewalls.

They say target use is internet of things. Makes for a great personal server too. I use a bunch of really small boards for fun, but not this small.

The pricing is on that page $39/each at qty 1000. I have seen the other models 2 years ago range from $50 to $70 at qty 1.