InfoWindow is a standard part of the Google Maps API v3, allowing the user to create a pop-up window on a map, but there's also two other libraries that seem to do the same thing:
I understand that these two most likely offer more customization options than the original InfoWindow, but are there any other differences? Are they competitors or do they do different jobs? Is one more up-to-date than the other?
While InfoWindow is the built-in object of the Google Maps JavaScript API, InfoBox and InfoBubble are "third-party" objects of the InfoWindow, which extend it. Because of this the two are located in the utility-library.
So they are doing the same job, but are more enhanced concerning customizations. The InfoBubble seems to be better documented and maintained. The InfoBox library is also not mentioned on the Google Maps Github site anymore. So if you have to make the choice I would go for InfoBubble instead of InfoBox (if you need more options compared to the standard InfoWindow).