Dragon+

Free to iOS, is Dragon+. It seems to be the newest rendition of the now defunct Dragon Magazine. It's free (for now) and can be acquired on iTunes App store. It is focussed on 5th edition Dungeons & Dragons. 

Love it or hate it, there is a lot happening at the moment regarding this edition, and for the hobby overall. There are plenty of reports of new players congregating to the hobby, and I think that's important. I for one really enjoyed my brief stint with running 5e, having at one stage close to 10 players at the table. One indication of a robust system is the ability for combat to keep moving, and even with that many players it did so well. 5e gets my vote even if I'm not playing it at the moment (I do own all the books). Being endeared with an OSR style of game I have been unable to escape the old school lure. 

But anyway if you're on iPhone or iPad you can download Dragon+ for free and access additional content pertinent to the 5e game, especially for their current Elemental Evil adventure line. 

More info HERE