I love that concept whenever any company comes up with it as a part of their marketing campaign but not sure what do we call such action.
The action starts with one tiny thing (say striking a small metal ball) and it hits another thing that swings further and does some action. The beauty continues and finally a big gate may open showing some message/greetings. So, a small tiny ball to a giant gate everything happens kinetically.
Here and here are two videos showing the action which is brilliantly crafted. I know the word 'chain reaction' but I've always used, heard and seen the phrase in a different context. Even the dictionary uses an example that does not fit to my concern.