I've heard mention of 'limitless' tickets in North America, either by bus or train. Do these exist? What are the conditions and prices?
Amtrak offers a series of USA Rail Passes; as of October 2015 they are
To discourage commuters from buying a pass (as opposed to a multi-ride ticket), travel is restricted to four one-way trips between any two cities and the cities in between them on the same route.
As with rail passes in most countries, these are for basic travel in coach class, so additional accommodations (e.g. sleeping compartments, business class) will cost extra. Also, the passes cannot be used on the Acela Express or Auto Train, or segments operated by some Thruway buses or VIA Rail Canada.
Two important caveats:
Greyhound used to offer a Discovery Pass, but this has been discontinued. The official replacement is to book individual tickets in advance, which is not really a replacement:
The downside is that "Going Greyhound" is not a byword for a speedy, high quality travel experience, though all the buses I have taken have been safe, air-conditioned, and relatively clean. I cannot say the same, of course, for many city bus terminals.