Yes, we have an iOS app. You can get it from the App Store.
Having problems with our app? This article might help.
Please note that while most books you can buy on Leanpub are also available on the app, some books are not. These are books that authors have created using their own tools, rather than Leanpub's book-creation tools.
If a book is available for reading on the Leanpub app, you will see a little "APP" symbol at the top right of the book's web page on Leanpub, where we show the book's language and the available formats.