A truly 3x3 monochrome font which covers all of standard ASCII with unique glyphs. This is the smallest monochrome font possible, since 2x3 or smaller doesn't have enough bits to represent the 95 printable characters. I've seen lots of 3x3 fonts, but all of them lack uniqueness or use descenders which extend the glyphs past three pixels in height.

The uniqueness constraint means some of the glyphs are rather awkward, especially symbols ($), numbers (2, 5), and lowercase letters (k, g, x). Also, due to the lack of descenders + uniqueness, some lowercase letters that don't have ascenders are three pixels high (c, g, p, q, y). Maybe it could be useful for a coding environment or a shell, where characters must be distinguishable (monospace might look strange, though).