Chicago O'Hare has a new single offsite car rental location you can think of as onsite Terminal 6 (no flights or gates). Terminal 4 has nothing; it's for future use. Rideshare users are told to go to Terminal 2 although there is a small rideshare area at Terminal 3. The El (metrorail; subway) to downtown is at Terminal 3.
If all this sounds complicated, their tram which goes from Terminals 1 to Rentals in order (and in reverse order) is of course crowded much of the time with all the folks going to Ride share and all the folks going to Rentals as well as the other permutations of tram trips.
Boston Logan has four terminals, one remote economy parking garage, a single offsite consolidated car rental, ferry & water taxi dock, and subway (metrorail) to downtown. There are shuttle buses serving different combinations of these locations and driving on the airport public access roads..