Looking to replace the boring paper hangers I had been using for my D&D party, I set out looking for screen-top initiative systems that allowed for marking when a character's turn was done. I didn't find anything quite right, so (several iterations later) here we are!
As combat begins, I call for initiative scores (in a Mercerian fashion) then place each flag in the array in the "down" position. That way there's some uncertainty about who goes when during the first round. On each turn, flip up the flag and off you go! During future rounds, I just start flipping flags down on each turn.
The flags slot in at an angle, and the tabs at the bottom prevent them from coming back out unless you pull them up to the correct angle again. They also lock in the "up" position on the center ridge of the tracker array, so they won't fall over if you bump them (lightly).
The "Array" should have plenty of room for all party members, NPCs and monsters in any reasonably sized combat, since there are 13 slots. That's the largest I could get to print on my Ender 3, and even that had to be rotated diagonally to fit. You'll want to print at least 3 clips to hold the array on top of your DM screen. I may consider revising the clips in the future, but these are working pretty well for me so far.
A couple of the smaller bits on the class designs may not print well with 0.4mm nozzles. I did try to scale up any necessary thin walls, but no promises. Let me know if any portions fail, and I'll see about improvements.
Print the array or single trackers as-is without support.
The flags should be printed on their backs.
The clips will require support, and should be printed on their side for best results. You may need to do a bit of filing to make the clips fit tight; I'd recommend gluing them in once you make them fit well.
Primer and Paint
I primed the flags themselves in white on the back and in black on the front using boring rattle-can primer, then painted a quick coat or two of white on the extruded class images.
On the back of the flags, I write the character's names in pen, just for reference when the flags are up and facing away.