We use a lot of little display cards in the shop and needed a nicer way of folding them than simply folding them by hand, which produces a very rough fold. Here's the answer - a creasing die based on what's used commercially.
The principle is to use a blunt knife-edge to force the card into a shallow groove to form a crease line on the card. It's then folded back on itself (a bit counterintuitive) to produce a nice fold line. The knife-edge used here is the backside of a piece of die-cutting rule, and is about 0.5mm thick. The card is also 0.5mm thick, and the groove is 1.5mm wide by 0.75mm deep - this seems for form a pretty good fold. There are various locating pins to position the card accurately each time and ensure the fold line is in the middle. The whole arrangement is mounted on the bench press.