1px-wide font

Millitext is a 'font' whose glyphs are just one pixel wide. But it's really a clever exploitation of how subpixels -- the individual red, green and blue lights of an LCD display -- are triggered by pixels of certain colors. For example, a magenta pixel triggers the red and blue subpixels, leaving the green one dark between them.
The result is as embedded above. Below is how the bitmap image would look like scaled up, on the wrong sort of screen—or simply as seen from a normal distance where the subpixels, as intended, appear to merge together.