Basically, a node that outputs the same output for any connected items upon being fired. Useful when one item has to trigger the same thing for several other items, and for changing what occurs without having to manually edit each individual connection.
So, instead of having to do something like:
Dice roll on 1 → Add 1 to counter 1, add 1 to counter 2, add 1 to counter 3, add 1 to counter 4…
Dice roll on 2 → Add 2 to counter 1, add 2 to counter 2…
…
It’d just be:
Dice roll on 1 → Add 1 to hub → counter 1, counter 2, counter 3…
Dice roll on 2 → Add 2 to hub → counter 1, counter 2, counter 3…
…
and changing the add to subtract would just require changing add to subtract on each of the hubs, rather than manually doing so for each counter.