Flash
Adobe Flash was the king of stop frame animation back in the day and unfortunately the player is being phased out in December 2020, which is a shame as many sites rely on the plug-in to run animation and video. I never really got the hang of ActionScript 2 as you can see from these examples here and to make matters worse the developers upgraded to ActionScript 3 for more influence with OOP! However, we did have tremendous fun with it!