We had a fancy coffee machine at an old job that ran Linux. If I remember correctly it was a top of line cafection or zulay machine. One of the ones with a touch screen. Just booted off an SD card as well iirc so probably would have been pretty easy to hack on.
I still find it weird that managed switches run Linux as I generally would think that at those data rates they'd need something closer to the metal but with the magic of HW offloading that's been a thing in enterprise for a while and OpenWRT even supports some consumer grade ones now.
Some (probably most) ebook readers like the Kindle.
EDIT: Totally forgot about these 2 ham radios. You can run and access Linux on both of these. One is by design as its running on a Pi, the other via mod by R1CBU booting the OS from an SD card.
It doesn't have as much to do with where the network stack is running, but that they're leveraging hardware offloading. Their CPUs generally aren't powerfull enough to switch packets at gigabit speeds let alone on many interfaces at gigabit or multi-gig speeds. Its by leveraging ASICs and maybe even some using FPGAs for hardware offload that they can switch packets at line rate. I understand how they do it, I still just find it kind of weird and cool.
I didn't list HDDs as someone else had mentioned that already. I was just listing a few devices that weren't mentioned in other comments yet.
Both really, you can't fully offload to hardware if your kernel still requires an interrupt to pass the payload. That hardware most likely has userspace drivers.
Software defined radios are kinda a stretch. The radio hardware isn’t running Linux. There’s a receiver that converts the signal to digital and then a Linux computer processes the signal. Basically the exact same thing as my computer having a radio receiver plugged in to it but packaged up as a standalone thing. If that counts, my keyboard runs Linux.