iOS: One of the annoying things about working with text on your phone or iPad is that properly formatting it can be a bother, especially when you're copying and pasting between apps and get line breaks where you don't want them. Clean Text for iOS aims to fix that. Clean Text is meant for people who work with a lot of text regularly and need perfection. You can find and replace words, fix line breaks and unwanted spaces, remove or add those annoying (well, depending on your preferences) "curly" quotation marks and convert HTML.
This is, for example, the kind of thing I might use if I were blogging from an iPad or even my phone, because I use a lot of applications and moving words from one place to another inevitably causes unwanted changes in formatting and styling. Clean Text helps clear up those problems so your words are just how you want them to be. It can't help improve your writing, though (as made evident by this post).
It's also available on Mac and syncs with iCloud so you can jump between devices.