Shrimad Bhagavad Gita This version of the Bhagavad Gita has loads of features, but is very small in size and won't hog space on your phone. It's in 7 languages, and is integrated with social media so you can share. Can be used offline.
Bhagavad Gita: Daily Message When you are looking for answers you can open this app and it will give you a daily message from the Bhagavad Gita. Works offline.
The Essence of Bhagavad Gita This is sort of like the Cliff's Notes to the Bhagavad Gita. Really helpful if you are just starting to learn about it.
Gita As It Is and Bhagavatam This is the entire version of the Bhagavad Gita in English and Russian. You can also highlight, add bookmarks, change font size, and it allows you to compare portions by splitting the screen.