Circa 2009 or so, my absolute favorite app for the iPod Touch was Patrick Collison's Offline Wikipedia (yes, that Patrick Collison: https://web.archive.org/web/20100419194443/http://collison.i...). You could download various wikis that had been pre-processed to fit in a very small space - as I recall, the entire English Wikipedia was a mere 2 GB in size. It was simply magical that I could have access to all of Wikipedia anytime, anywhere offline - especially since the iPod Touch could only connect to the Internet via WiFi. It was particularly useful while travelling, since I could load up articles and just read them on the plane.
As I recall, there were several clever things that the app did to reduce the size of the dump; many stub/redirect articles were removed, the formatting was pared down to the bare minimum, and it was all compressed quite efficiently to fit in such a small space. Patrick gives more technical detail on an earlier version of the app's homepage: https://web.archive.org/web/20080523222440/http://collison.i...
As I recall, there were several clever things that the app did to reduce the size of the dump; many stub/redirect articles were removed, the formatting was pared down to the bare minimum, and it was all compressed quite efficiently to fit in such a small space. Patrick gives more technical detail on an earlier version of the app's homepage: https://web.archive.org/web/20080523222440/http://collison.i...