Phraseology is an app I’m going to recommend my EAP writing students check out. (I’m an Android user, and this app is only available for iOS, so I can’t check it out myself for the moment.)
The first interesting feature this app offers is a facilitated editing environment which shows the use to drag and drop to rearrange sentences and paragraphs. I find structural editing on a tablet quite frustrating, so this really caught my eye.
Phraseology also provides a host of statistics on your text. It can colour-code your text by part of speech, something particularly interesting for lower-level writers. It also gives readability stats; while there are other programs and websites that offer this, having this feature in app saves a step, and makes it easier did students to monitor and strive to up the grade level of the texts they produce. Word frequency breakdown is another tool that quantifies lexical variety and complexity (or lack thereof) in a text.
Complexity and variety of word choice figure frequently in the types of comments we give as writing instructors, and having some type of quantifiable indicator of these textual features can help reinforce our comments, and support students add they carry out independent work on these aspects of their writing.