Across the years, I have found a number of things that might be 'free energy' or overunity.  I will use those terms loosely, I would consider a triggered radioactive decay into electricity to be 'free energy', in effect.  A second thing to be considered is answering the question, 'how could 'free energy' be hiding here and not be noticed by scientists?'


1) Electrical discharge devices - Correa, Kapanadze, Gray, and much more.  I don't think all discharge phenomena has been fleshed out in detail.  Indeed, the Correa patents suggest that strongly.  The more transient and ordinary something seems, the less likely it is to be investigated to find a 'surprise'.


2) Table top transmutations - Cold Fusion, Adamenko, Shoulders and more. In particular, ignoring the depth, breadth and deep background of Shoulders is just crazy.  There is 'something' here. Of course, disbelief in such a thing is mostly automatic.


3) Centrifugal devices - Schauberger, Linevich, and more.  Does mass change briefly in acceleration/deacceleration?  Kosyrev and a French physicist thought so.  This subject is dismissed quickly by saying 'pseudo-force'.


4) Cavitation and Water Discharge - Schaffer, Papp and others.  Nobody can explain cavitation but it exists.  Papp was dishonest but he had 'something'. 


Honorable Mention Inventions - things I can't explain either as science or fraud.  Even "Penn And Teller" can't explain All magic tricks !




Moray - maybe a VLF resonance with the ionosphere.  Hard to dismiss the stuff he did. 


Coils That Weirdly Make Electricity - some of which I can't figure out as fraud. How?


The above is not comprehensive.  Just areas to examine, IMHO.  I do think there could be things 'hiding in plain sight', as yet unnoticed.  I frequently find facts exposed on Quora that I am shocked that I never knew about major events.  It can happen.