These originated as flats that were folded and sewn that way. This saved time by cutting out the step of folding a flat diaper in this basic pattern. It has fewer layers on the sides and more in the middle, putting absorbency right where it's needed. They can be found in multiple sizes and the number of layers can vary based on the brand or size. Many of today's adults wore tham as children.
The difference is that today, sharp pins are outdated and the hated rubber/plastic waterproof pants have been replaced with a variety of much more convenient and baby friendly.
You must use a diaper cover over this to keep it waterproof.

Prefolds by Curious Crayon

Handmade of 100% cotton fabrics. These come in the standard sizes of each fabric. An alternative sewn-in soaker is available in thick terricloth, microfiber, and flannel. Custom orders can be made in a requested color or pattern.