I make no secret of my affinity for small keyboards—I don't even own any full-sized boards anymore. Once you get under 40% (like the Minivan), you're not really talking about a replacement for a larger board. Sometimes, that's not the point. There are mechanical keypads and even smaller devices called micropads. One of the coolest micropads I've ever seen is the RAMA M6-A, which I've had a chance to play around with over the last couple weeks. It's an extravagant luxury for the discerning keyboard enthusiast.
There's no hard and fast definition of what constitutes a micropad, but I'd say it's anything smaller than a number pad. The M6-A, as the name implies, has just six keys. You can use those six keys to do almost anything you want. They can be single characters, modifiers, or even macros.
The online firmware manager "Knops" makes it easy to build new layouts and flash them to your keyboard. Since this is entirely self-contained firmware, the M6-A works the same no matter what computer you plug it into—it'll send whatever keycodes you've programmed. For example, I have mine configured to put my PC to sleep, show/hide the desktop, open the task manager, split screen my last two windows, and more. Sure, I could do all that manually, but it's neat having a little mechanical pad that does it with a single press.