Craneflak, Brain-Flak Classic, Rain-Flak, BrainHack, Brain-Flueue, miniflak, miniHack: .1020

(([]()()()<()()()>)()()){}#{}({}()) 

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Explanation

The first thing going on here is that there is a difference in the way comments are read between the BrainHack, CraneFlak and Rain-Flak interpreters. Craneflak has no comments, in Rain-Flak # comments out the rest of the line and in BrainHack #{...} comments out the insides.

So here's what each language reads:

Rain-Flak: (([]()()()<()()()>)()()){} -> 3 BrainHack: (([]()()()<()()()>)()()){}({}()) -> 4 Craneflak: (([]()()()<()()()>)()()){}{}({}()) -> 1 

The next thing is the difference between the brain-flaks and the miniflaks. Both Rain-Flak and BrainHack support miniflak, where all of the extra operations are simply removed. This means that they lose the [] and <...>

Rain-Flak: (()()()()()()) -> 6 BrainHack: (()()()()()())({}()) -> 7 

Next we have the difference between Brain-Flak and Brain-Flak Classic. In Classic [] is -1 instead of the stack height, which means that our result is 1 less than in regular Rain-Flak, making it 2.

Lastly we have the difference between brain-Flak and brain-flueue. In brain-flueue a queue is used instead of a stack. Normally brain-flak pushes 3 then 5 and pops the 5 away, however in brain-flueue the pop gets rid of the 3 and not the 5.