Nine-pin's diamond
Traditional nine-pin bowling arranges its pins in a diamond rather than tenpin's triangle, with a distinctively marked center pin. The game has deep roots in continental Europe and was carried to the Americas by European immigrants, where it was hugely popular in some communities. The shift toward ten pins in America is often told as a response to attempts to restrict the nine-pin game — adding a pin sidestepped the rules and, in the process, created tenpin.
Team play and tradition
Nine-pin today is frequently a team game, with a lively league culture in parts of Europe and in pockets of America where immigrant communities kept it alive (Texas being a notable example). It's social, tradition-rich, and played in clubs that have maintained the game for generations.
Skittles
Skittles is an umbrella term for a family of old pin-toppling games, especially associated with British and European pubs and villages. Variants differ wildly in pin count, equipment (some use a ball, others a thrown 'cheese' or disc), and rules — a beautiful illustration of how local rolling-and-toppling games proliferated before standardization. Many skittles variants survive as cherished local pastimes.
Why they matter to us
Nine-pin and skittles are the living link between bowling's ancient origins and the standardized modern game. Understanding them makes clear that tenpin wasn't invented from scratch — it was selected and standardized out of a rich, messy family of folk games, most of which still roll on somewhere. That's the whole reason this section exists.