There's a whole subculture for fonts smaller than 8 by 8, with real world uses for things such as small LED displays, for example. This is at the extreme end, though.
That’s really more of an encoding than a typeface. Like ASCII and Unicode.
But I guess if you can build fonts that generate barcodes, and fonts that have LLMs built in, then you could design a 1 pixel high font that uses Morse code to represent most ASCII characters.
I wonder if there are really tiny fonts that make use of color. For example, this 2-pixel wide Picket Right font could theoretically be even thinner if we were to use sub-pixel features.
At least, I think the 2-pixel high Two Slice font can be more legible with some anti-aliasing.
Don’t stop at colors. Just add a ligature for every string and support for animations and you have yourself a font that can render any alphanumeric string in a single pixel. I’ll need to brush up on Morse code though.
With the gap, it's effectively three pixels wide. Basically a 3x5 font with one pixel chopped off.
On some displays, you can also divide RGB into three subpixels (R, G, and B stripes). A 3x5 pixel font (9x5 subpixels) can be drawn as a 6x5 subpixel font instead (a 2x5 pixel font).
Not sure about one font vs the other, but that one seems easiest to read from a highly oblique angle since that makes it look more similar to what it would do if half wasn't missing... Unless I'm just gaslighting myself and find it easier to read that way because I was expecting that it would be easier!
Pad grid controllers like the Novation Launchpad, and its indie, open-source counterpart, Mystrix Pro, have an 8x8 grid. At first this style of controller didn't use any lights, but as the manufacturing and features progressed, they went towards one RGB LED per pad. So, of course, you end up doing some text and graphics on the resulting grid. Mystrix uses a scrolling marquee which isn't ideal, but does get the job done.
And yeah, you could throw on more hardware to have a display nearby and use that for text. That is not the problem being solved though.
By using the three available colors on my older model, I was able to render numbers up to 199 in a readable way. Two digits on the right are 8x3 and one on the left is 8x2. I quickly abandoned two pixels of width as impossible for making legible text for all digits, so seeing a full font at two pixels wide is a fun surprise.
Also https://stormgold.itch.io/picket-right-font