A way for players to keep track of what they have done/not done yet. And for the GM to track this if they want. I know it's just 5 things. Action/reaction/bonus action/free action/move. But i have seen enough players, myself included, forget an available reaction or accidently double bonus action, or need to back track the turn to try and remember if they did use the bonus action already, and so on. Some GMs might just want to keep track of this. I've heard plenty of polite GMs remind a player they have an unused option. A tracking tool for this could help lighten a little of the load for some. One a player could use would also display their status to the GM. And for the GM they could choose to show the tracking tool for whatever players they wanted to on a player by player basis. Filling it in themselves for players not using it if they wanted to tack it. Something not too big, but large enough to also be a visible reminder, you do have a bonus action to use, you have already used your reaction. It's a play aid like that. 5 icons to represent the 5 action options. That flip to show "used" or go from green to red, or whatever when clicked on. Resetting on manual button press or use of turn tracker/initiative tracker to notice your turn has come back round. Thanks for the consideration. P.S. At the IRL table i offer 5 poker chips each to the players. With with the action options printed on one side and "used" on the other. I notice it helps turns move a little more smoothly and those who use them seldom forget an option they could exercise.