Hi Sarah - I think I first saw this in Japan years ago - they do these for melons as well (honeydew and stuff). They also have star shaped and heart shaped cherry and grape tomatoes

supermarkets near the uni and young professional rental flats usually have the kawaii shaped maters.
The molds are usually made from repurposed wood from crates/pallets. The mater moulds tho are expensive plastic or silicone types. I don't know whether they had any luck with boxing in squash and pumpkins but they were trying to do that way back then.
Update: square squashes and pumpkins also common there nowadays as well as cubecumbers and cube bitter melons - wonder what's next.
Update II:
Sarah - I believe I will be dreaming of putting all of my limes and lemons in "citrus corsets!"
http://www.withheartandstar.com/homeStar-shaped moulds? That's a five point shape, perhaps a four point flower shape would sell better esp among female gardeners.