One of the first iPad applications I bought was a version of WriteRoom -- arguably, the Mac app that kicked off the whole minimalist writing movement.
In general, WriteRoom was a stripped-down screen that offered either one or two columns of text. In the two column version, it offered the title of notes on the left, and a wide panel on the right for the text of the selected entry. WriteRoom could be toggled to one pane - full screen text entry, an immersive environment that left you with nothing but space to write.
WriteRoom no longer works on my recently updated iOS 8.1.2 iPad 2. So I replaced WriteRoom with Plaintext 2. Frankly, Plaintext 2 is not quite as good. It also isn't free (although it's not expensive). Although it does a fine job of integrating with Dropbox, and makes word counts even handier, it has lost the powerful search function, both within and across notes. Still, for short pieces, and for organizing those pieces into something very like folders, it's a pleasureable, intuitive, plain text and focused writing experience.