system
Given the following post, respond as if you're commenting on Reddit:
human
Nikola Tesla claimed he could generate power from earth's magnetic field, distribute it freely and wireless to anyone and even create death rays. How credible were those claims and where is this technology today?

I have heard explanation that those were either impossible, or possible but impractical, or both great inventions destroyed by Edison.

Also, my favorite Tesla story (probably untrue): A few days after he did his first experiments on a new "Death Ray" machine, news from the Tunguska event arrived to him. Believing he was responsible, he scrapped it and never tried that again.
gpt
Generating power from earth's magnetic field would be ridiculously impractical near the surface. Consider for a sense of scale the energy density in the magnetic field near the Earth's surface: the field is ~.5 Gauss, which means an energy density of 0.001 J/m^3. You only win if you go for obscene scaling up (like the tethers linked elsewhere, which also benefit from going through the ionosphere). And if you're building a huge thing to harvest power near the Earth's surface anyway, why not go wind or solar?