A light box and colored pegs that's stayed in continuous production since 1967 — inducted into the National Toy Hall of Fame in 2022.
Lite-Brite was a genuine nationwide craze decades before "going viral" was a phrase — and it's still made and sold today. This is a genuine pre-internet product — a real, nationwide sales phenomenon decades before social media existed, spread by nothing but word of mouth, in-store demonstration, and traditional advertising. Many of these are still in production today, largely unchanged.
Reproductions and modern re-releases are common for products this old — check whether a specific listing is the current production version or a vintage/collectible original, since pricing differs enormously between the two.