WikiVoyage Offline Travel Book is out with a new Android edition available at Google Play.
There many apps, online and offline, that collate various travel flavors of Wiki- sites. I have not tried them all (and one for Apple iOS). This one is road-tested and I like it.
Having solid offline functionality is key to travel. Even where we have connectivity, a solid offline resource comes in handy at those crucial moments where connections drop or are too slow.
WikiVoyage has extensive listings across the globe. Most useful to me are current logistics information such as airport transport.
New editions come out a couple times a year. The file is 576 MB so is good to download before a trip starts. If you have the prior edition and device is running low on space, uninstall it before installing the new.
Readers, what offline Wiki or other travel resources do you use?