OSes for old (really old) PCs

It's amazing what can bubble up from forums; consider this: Operating systems for really, really old computers from the Ubuntu forums.

What a great list! The poster (darrelljon)  lists a few dozen little operating systems, mostly but not all Linux, that are small and light enough to run on older computers. Sorted by size, and in subcategories depending on what media they'll fit on. With links! Awesome!