Short answer: No, not plausible.

That web page is incredibly confused. At one point it talks about a "scaler EM weapon" and at another point about a "particle beam weapon." It brings up Tesla (his supposed magical inventions - as opposed to his significant real contributions - have become almost as big a part of myth as fabled Atlantis).

You could conceivably build a (very bulky) gamma ray weapon that could kill people through irradiation. Or you could do something similar with neutron radiation (such as with enhanced radiation bombs). In both cases, you can shield against it, though it might require substantial shielding.

You certainly aren't going to have a simple ray gun. A nuclear weapon, that blows up like a typical (though low yield) nuclear bomb, sure, that can be done. Or you could kill somebody using an immensely bulky cobalt-60 gamma ray projector, if you could get them to sit still for you. It wouldn't be a practical weapon.

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