In the “good old days”; i.e., pre-deregulation, if your flight was cancelled or you missed your connection due to some act or omission of your carrier, you merely walked up to the counter and asked for a “Rule 240” ticket on another airline at your carrier’s expense. Barring that, your carrier would put you up in a hotel overnight for free.
Deregulation of airline travel allowed most carriers to quickly do away with Rule 240; but a vestige of the rule remains in some carriers’ contracts of carriage.
The folks at airfarewatchdog.com have done the research for you and come up with a nifty chart of the current provisions, if any, which require the airlines to get you to your destination after they fail the first time.
Hat tip to aviation.com.