Pantone Color Web
ColorWeb pre-dates inclusion of "web-safe colors" in programs like Photoshop. It gave you the subset of web-safe colors right in the computer, without having to look on a piece of paper or anything. It came out very early in the web craze, so was useful for a few years before everyone caught up, and video systems became more capable.
I sorta miss it, actually. Though it was an add-on program, and therefore in places like Photoshop or Painter where you usually use the app picker, not the OS one, you had to switch over to get to it, it was well-organized.
It was (past tense, as its so old you cannot run it on modern computers) arranged in a unique, but usefully perceptual scale, and overall was like any other Pantone color picker.
The silliest thing is that it had a swatch book! A normal Pantone swatch book, but very thin and... it's an RGB-only standard. I never could figure out what they thought they were matching the paper samples to.