My favourite initiative tracker is a piece of paper and a pencil. Write down the initiative numbers with the names of the character. Go down the list. If you have trouble keeping track of where you are, mark it with the pencil, possible by crossing out the initiative that's been used. End of the initiative pass, write down the initiatives for the next pass in the next column. Update initiative with it changes. Keep plenty of space around everything so you can write more down in between everything, like the damage of various grunts and status effects.
It works very well for me, but you need to keep space and mark down everything.