A lot of designers are starting to use Sketch. I've played around with it for a bit and I found it much more straightforward than Photoshop or Illustrator (given I'm not a designer). Plus it's cheaper and less resource intensive. I also like that there is a couple of sites where people share their projects, e.g.
or
That being said, it has a couple of bugs which if you run into are annoying but in no way a deal breaker.