I'm presenting here a pocket-sized puzzle in the first of several versions, depending on your skills, materials, tools and target audience.
In every version, though, you drop a small coin in one slot, and need to get it out of the other slot.
This first version is quick and easy to make (it took me less than thirty minutes from idea to finished item), and small enough to keep in a pocket. It is also perfect for making with children, as a diverting way of filling an afternoon.
Step 1: Materials
To make the "easy" version, you need thick card, something to cut it, and something to glue it. If you are using a craft knife to cut the card, a metal ruler is also very handy.
The card needs to be as thick as the coin you design it for.
Almost any glue will do the job - PVA, glue-stick, etc.
Note: when it comes to cutting out the parts of the maze, a laser cutter would be very handy. It would also make it a lot easier to make larger, more challenging versions.