The classic Rubik's snake (Magic Snake) from the 80's!
For those who don't know how it works: it is possible to rotate each segment relative to the other one at 90° intervals. The idea is to "fold" the snake onto itself, creating complex figures.
Print the pieces on their wide face (the hypotenuse of the triangle).
You will need to print one head, one tail and as many body pieces as you like, although the snake will work best if you use an even number of pieces (24 works very well, being divisible by 2, 3, 4, 6, 8 and 12).
Traditionally snakes comes with pieces of alternating colours (there are some nifty effects that can be achieved with this, when folding the snake.
The pieces have their own support built-in. It's just a tiny column supporting the pin (male connector). The surface where the support touches the piece won't be visible once the snake is assembled, so - provided the cut is flush - you don't need to obsess over leftover marks.
My wife bought this toy for one of our kids, but the toy broke within minutes (it was kept together by a plastic wire passing through all the pieces), so I built a new one.
I knew the toy under the name "Magic Snake" so I initially did not find a ready-made model, but if you search for "Rubik's snake" you will find several other designs alternative to mine.
This is one of my very first designs, any feedback on how to improve is very welcome! :)