I'm honestly not sure who first might've attempted something, but the first that comes to mind was an attempt by builder Sol3kill3r. In typical fashion, I'm not having any luck finding pictures of his launcher. I wish I remembered more of the history here, because I'm guessing someone else might've made their own attempt, and then I was motivated to try something. My first attempt was awful.
I aimed to make something compact but the result was something that looked ugly and barely worked. Still, the one innovation I added was a horizontal magazine for single-slot connectors + green rods. This saved me the effort of cramming a vertical magazine into the body somewhere.
Recognizing that the folding functionality of it was just not worth it, I decided to expand on the horizontal magazine concept instead. The result was something that looked a bit more appealing in my opinion.
It was in the form of an oversized pistol. The magazine was lengthened to hold more ammo. It got a little better range from a fuller utilization of the striker length too. It was a cute concept but still not all too practical, so I never did end up posting it. At another point, I did try making an even more compact horizontal magazine launcher design, but it was challenging to make something up to my design standards of the time. Perhaps it's something I can revisit. And here's another slightly cringey video of it in action:
Later on, someone else would try to make a more compact folding launcher, the most compact one yet, so me being me, I took it as a challenge to make something even smaller. My first iteration used a more traditional vertical magazine for single-slot connectors + green rods. Sorry for the awful picture quality.
I believe someone suggested I try using Oodammo since I was so familiar with it. So I slightly redesigned the launcher.
The resulting launcher only had a four-round capacity, but it was novel for being the first and only folding Oodammo launcher. I was also proud of how compact it was at the time, though it came at the expense of the handle design. My design also never automatically unfolded like other designs, it required manually deploying it. Here's a slightly less cringey video of it in action:
I've toyed around with ideas for other folding designs, but they're just so tricky. The more compact you want to make them, the less capable they generally are. But in my opinion it defeats the purpose if you make a large design. At the end of the day, folding designs are just a novelty anyway.