There's no app, but as long as you're using a tablet and probably a plug-in keyboard, you should be able to use the online version of twine 2. There's a downloadable OSX version http://twinery.org/
I managed to sorta use it on a phone (android), but it needs a bigger screen.
It's open source so you can make an app if you want, but it costs £100 last time I checked to put an app in the app store, which includes a bunch of testing. So go ahead if you want.