It was an experimental test to make an app compatible with that site but it failed. There is no working app for the site. Especially considering the NSFW content here will be shot down by Google Play and the App Store.
I been looking for quite some tine for 1 , but there doesnt appear to be a single one that is working even remotely properly .
The site displays just fine on mobile as is.
Derpibooru costs over $25 a day to operate - help support us financially!