Having previously looked at Dictionary and News apps, I'm now going to cover apps for learning or practising grammar.
As far as free/cheap apps go (the type we prefer!), the choice is disappointing. Or rather, there are plenty of apps, but very few worth the trouble of downloading. Here are a few which are.
• 10 Minute English teaches intermediate-level learners of English using realistic audio dialogues between native speakers of English (British English and American English). The dialogues are structured around grammar points which intermediate learners usually have difficulty with. The grammar used in the dialogues is fully explained in simple and clear terms. The free 'Lite' version has three lessons, while the 'full' version costing $4.99 has ten.
• Grammar Girl Podcast App ($1.99). One of the very best ELL podcasts delivered right to your iPhone along with a weekly bonus audio file that covers an additional grammar or writing topic. Bonus tips are only available through the app. You'll also occasionally receive free book excerpts. Of course, you could subscribe to the podcast on iTunes for free, and transfer it to your iPhone, but $1.99 is a small price to pay to avoid all that hassle and get direct access to over 200 podcasts.
• Mobi Bac Terminale Anglais (free). Excellent grammar reference app for French speakers. Covers all the main grammar points and gives tips on preparing for the Baccalauréat oral and written exams. No exercises, however.
To get a grammar app with a full range of practice activities and exercises, you're going to have to pay a bit more.
• English Grammar in Use Activities ($9.99) Based on the best-selling grammar book by Raymond Murphy. Designed for intermediate level learners of English. Over 2,800 questions, divided into 16 grammar sections. Features a variety of activity types. Audio recordings of all the exercises. Record and play back function.
There's definitely a gap in the market for a decent grammar reference app.