Yes, we have apps for Mac and PC, iOS and Android.
To learn more, see our Apps page: https://leanpub.com/apps
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.
Finally, if you are having problems with our iOS app, this article might help...