Here is a sample using arrayMaker to illustrate what aliessmael example: that is storing object colliding with a collider ( I will use triggers here, but colliders would be identical).
to install this example, first get arrayMaker here: https://hutonggames.fogbugz.com/?W715
then you can lod this package. It will overwrite the gameObjectPositioning scene in PLaymakerSamples/TestLab/Addons/ArrayMaker/ArrayList/
look for the gameObject named "cube trigger"
I have several cubes falling. I created a plane "cube trigger" right in the way of the falling cubes, I set it's collider to trigger, and with one fsm and two actions, I have a system that detects the cubes and store them in an array. I have also added an array list to that gameObject ( to do so, select your gameObject, and click on the menu "playmaker Add ons-ArraMaker-Add ArrayList proxy to selected gameobject" )
Now play the scene, and watch the prefill content of this array getting all the cubes that fall through this plane. Also, notice that you'll get duplicated items because some cubes bounces etc etc. so as an exercice, you could check if the gameObject is already in the array ( using ArrayListContains action ) and if not add it
I don't really see this as being complex if you actually come to need to work with arrays in your game,
-- but I appreciate that the lack of help for arrayMaker does not facilitate the task, and the action interface inability to be context based ( that is I have to display all the possible fsm variables, that is not helping clarity too...),
I would not build a specific action ( I only had to use two actions here) for this, because it would be so specific that it would unlikely be reusable ( and actions should be reusable as much as possible). For example one purpose would be to record activity, while the other would be to store and sort a list of all objects that passed through it wihout duplication, another use would only require to store a component from the gameObject, or a particular property of that gameObject. So really, in such cases, I think building the logic using states makes more sense than building a single action.
I need to find the time to do the arrayMaker documentation ...