Haven’t seen this discussed here yet but this looks like an interesting piece of technology: https://korgnutube.com/en/
It’s a small, low-voltage, dual directly-heated triode device. It’s manufactured like a vacuum fluorescent display, just with “one pixel”. Despite the size, it shares audio characteristics with traditional valves.
While you can buy the triode yourself for about $50, it’s been steadily appearing in KORG products since its 2016 release. Some interesting ones:
nu:tekt OD-S Overdrive pedal kit
The pictures of the last one is actually a unit that I assembled. The overdrive is suitable for both guitar and synthesizers, can provide clean boost as well as pleasant low-gain distortion. Thanks to the low-power nature it’s perfectly happy with a 9V battery which makes it a unique stomp box. If you’re interested I can make some demos.
It would be cool to see it used in eurorack modules or in conjuction with NTS-1 or the bigger Minilogue xd. There’s already an interesting DIY project with this device: a preamp. Note that unlike the OD-S, this is an actual soldering project.