We do not have a mobile app, but Write & Improve, which is a web app, works on all devices. You can use it on your laptop, desktop, smartphone or tablet, and if you create a profile (it's free!), all your work will be saved and you will see it on all your devices.
Did you know, you can create a shortcut to Write & Improve on your smartphone or tablet homescreen so that you can open it with just one touch, like a mobile app? For Android devices, just open writeandimprove.com in your device's browser, then touch on the menu, and choose 'Add to Home Screen'. On iPhone, iPad etc., go to Write & Improve, then touch the Share button on your browser’s toolbar — it's a rectangle with an arrow pointing up. It’s at the top of the screen on an iPad, and at the bottom of the screen on an iPhone or iPod Touch. Choose the Add to Home Screen icon in the Share menu. Now you can open Write & Improve with just one touch.