And are you sure all countries allow you to "reside" there and work, even though your clients are outside of the country, and the payments are being made into a foreign bank?
I think grandparent's question is legitimate. In most cases the authorities probably don't care much how tourists (or, people with tourist visas) spend their time, but I also wonder if all these nomads follow the letter of the law to the dot -- which would be a feat with the laws of 78 countries.
Most certainly not following the letter of the law, but it also just doesn't really matter. Don't overstay and don't tell them you are working when you try to enter on a tourist visa and its not really possible for you to have any problems.
If you do, just leave without making a fuss.
Things become more complicated if you decide you want to stay permanently somewhere while working remotely. Then it depends on the country and how much crap you're willing to put up with.
I think grandparent's question is legitimate. In most cases the authorities probably don't care much how tourists (or, people with tourist visas) spend their time, but I also wonder if all these nomads follow the letter of the law to the dot -- which would be a feat with the laws of 78 countries.