There are SD cards with WiFi support

I still use a 16 gb one for my DSLR. When I bought it about 7 years ago, I opted to get an older entry level canon which was basically better specced than the current (at the time) entry level model and far cheaper. The new model did have wifi though so I got one of these. Works pretty well. And other apps support them not only their included one (PhotoSync on iOS comes to mind). They are slow AF but get the job done.

Yup. It was used to transfer photos from a camera to a phone back in the day when cameras didn't have wireless transfer features.

They’ve been around for a while. I used one with a 5D MkII several years ago. Horrible throughput. It was only useful for a quick transfer of a few images. Totally unsuitable for field dumps.
Had one for my iPaq in the early 2000s.

I had good luck with these at my wedding. Instead of disposable cameras, I put cheap digital cameras. It didn't take long for guests to realise that the pictures were appearing on a large tv, in a sideshow. People got a lot more creative when they realised they would be seen quickly, not weeks later.

I managed to get them working without proprietary software, too. The onboard script logged into WiFi and uploaded the photos over ftp.

Given their size and the level of tech at the time, it was pretty impressive.

I'd be so thrilled if I was at a wedding that did that. Cool idea.
- We also set up an excellent photo booth with the same setup.
  
  A DSLR, on a tripod, a cheap remote trigger, and some photography lamps. We used drapes to box it off a bit. Throw in some inflatable props, and let the kids/drunks make it awesome.
  
  The photos on the TV just encouraged others to join in the fun.
That's awesome
What year?
- Less than 10 years ago, though they were getting obsolete at the time.

I recently looked into them. They seem shit. Dodgey outdated apps to make them work and such.

Too bad it should be the simplest way to add wifi file transfer to a 3d printer
- I'd rather just have an ethernet port on the damn printer. You shouldn't have to cludge together basic network device functionality on devices that expensive
- If you're interested and can get your hands on some kind of SBC (like a raspberry pi) Klipper has been amazing for my printer. You can also use pretty much any computer but it'll be much less efficient energy wise.
I tried them with a few different cameras. They sucked. They wouldn't reliably connect to Wi-Fi, and they didn't reliably upload images.
That's another reason why they're kinda dead now. Closeted apps they have to maintain just to keep that garden walled, and it was a cost they decided they also didn't want to spend.

I still have a 4gb Eye-Fi that use just as an SD card to shuttle files out to my laser cutter. I assume the wi-Fi would be horrendously slow and insecure if it worked at all. Was pretty cool when we still had a standalone P&S digital camera though.

Things like this would be so useful in the tinkering community, so many motherboards and such use micro SD cards or USB drives as a primary storage device. Before I gutted my 3d printer and put a computer inside it, I had to schlep the micro SD card back and forth from the printer to the computer room.. being able to send it wireless would've been great. Looked into it at the time but as other have said all the current solutions are dog shit.

Well, Octoprint worked well for me.
- Oh I'm way past octoprint and have advanced to klipper, it just would be nice for similar applications, or for people who don't want to set up something similar.
- I had a much better experience with Klipper once I got it up and going
- Doesn’t octoprint need a computer inside the printer though?
It seems like somebody already thought of that.

Yep, had one for my Treo in 2006

Still use mine in my cannon point and shoot. (Just as a storage device though) The software support has long ago suckified when "cloud" became all the rage, but it was awesome to sync camera <-> PC without messing with adapters or cables.

Things like this were huge back in the days of PDAs. They had SDIO ports specifically for expansion. I had one for Wifi and another for Bluetooth on my Garmin PDA, so I couldn't use Bluetooth and Wifi at the same time, and both kept you from having non-volatile storage. If your battery died, your system was wiped because all the storage was in memory.

I got a Dell at the very end of the PDA era (the iPhone was already out, but was still ATT exclusive) that was super fancy because it had a CF card slot AND an SDIO port, so I could store data AND use my SDIO digital camera.

Was it the Axim x50? That was a fine looking PDA. I had an Axim x30 and loved it to death. Its death. Then, I got an IPAQ 210. They didn't have any good accessories for that one. No clip on thumb keyboard or anything.
- I don't remember the model at all. I didn't use it very long, as I ended up getting a Blackberry a few months later, and between it and my laptop I really didn't need a PDA.
  
  I used the Garmin iQue m3 for years though, since I had it earlier and it had a pop-out GPS antenna that kept it useful as a navigation tool in the car well into the 2010s.

The old Toshiba ones could run a WebDAV server on them and you could log in with a PC and upload files. Was pretty sweet in a flash cart.

So what does it do, exactly? Can it act like a NIC or something?

Acts as access point, if you connect to it from another device you get access to stuff on the SD card (via app or built-in webserver)... at least in theory. Quality varies.
Most of them act(ed) like an access point.

However, the SDIO spec allows for cursed applications like WiFi adapters, Bluetooth dongles, and more to be fitted into an SD card. It was really just SPI, so in theory it also allowed things like GPS tranceivers and any other peripheral you can think of that's low bandwidth enough to work over SPI. Need Bluetooth for your Palm PDA? Here you go! Just stick a massive slab of plastic into the SD card slot!

These days SDIO is only really used for alternative (faster) transfer modes and maybe some slow and insecure WiFi access points in cameras.
Mine acted like a wifi card. I could connect to wifi networks with it.

Worked for shit, but it did work... Just enough.
That’s not what is pictured here, but yes NICs that talked over SDIO were a thing in the days of PalmPilots and iPaqs.

I thought it was cool.

CompactFlash, too. I 'member looking at them for a Dell PocketPC I found at a garage sale.

I had an early PDA (think it was an IPAQ, not to be confused with ipad) that had a 56k modem that connected via CF slot.

There are also horseless carriages.