Tesla was one of the worlds greatest inventors, a man who could both create in theory, and pactice. Tesla did not claim at first that he could create or capture "free" energy, but that he could transmit energy wirelessly (remember radio was in it's infancy here, few people would have one of thier own). He then later began to claim that the there was always energy present that could be captured/converted.
To some extent this has been tested and proven, BUT the energy required to build the equiptment is far greater than the energy the system will return
For example, if you build a crystal radio (not having or needing any batteries) and then listen to it you are hearing the radio waves being captured by the radio and converted to sound waves (which is motion in air). You have just created free energy, BUT it will have cost thousands of times more energy to create the device, than the device will collect.
Tesla belived that there was another better way, that had to do with matching frequencies and harmonics, that no one, not even Tesla ever proved (proof being = accepted by scientific peer review). Some people now claim that they have figured this out but all seem to be unwilling to have thier claims peer reviewed. The water power people are a great example of that, they claim big companies keep these things secret, but if that's the case is China owned by big companies, why did they build the three gorges dam? because they are too dumb, or are they controled by the big companies too? I can run my car on water, I just build an electrolitic cell to split hydrogen from water, allow it to recombine in the engine and drive my car.... but if I had just used the energy in the battery to drive an electric motor I would go a lot farther, lots and lots......
I don't remember Tesla's flying machine? but I am familar with most of his other inventions. His radiant energy system was first based on using radio frequency energy emited from a tower he constructed using the earths ionasphere as a wave guide to keep the energy from escaping into space (like AM radio), then collected by users where needed. He later made claims about not needing to radiate energy. I think it needs to be said that in the end he was a bitter man. He spent the later part of his life poor, watching people who made millions off his ideas prosper. He had all kinds of reasons to make extrodinary claims that could have been untrue, which is what seemed to happen near the end of his life. It is true though that some of his work still isn't very well understood, so ?????? I have looked at many free energy claims and not found one belivable one, I do belive that it may be possible but I have looked at all the possilbities that I can find including the previous video answer and don't find them credible.