Android: Wikipedia's mobile app (and site) have always lagged a bit behind modern mobile conventions. Today's new beta app, however, is a huge leap forward in the right direction with sweet new slide-out navigation panels and a lot of other new features.
Unlike many other Android betas, you can download this app directly from the Play Store and run it alongside the regular app. It includes the increasingly-standard hamburger-style slide-out navigation panel on the left side and, when you're on an article, you can slide in from the right to reveal a list of sub-sections. You can also translate articles, save them to your bookmarks, and review your reading history. If you fancy yourself an editor, you can even log in and edit articles directly from your phone.