I tend to collect software. I read about things that people I follow recommend and if it's free or affordable and looks interesting I'll usually get it. It gives me an opportunity to look at different paradigms, recommend alternative software to students who might be on different platforms than what they use at school, and generally nerd out.
As a result I have a bunch of graphics software sitting around either in the Mac App Store or installed on my laptop (mercifully the Adobe suite is licensed through work so I don't have to buy it myself or make space on my own machine). When it came time to sit down and "design" (the air quotes are deserved) the graphical assets for Repeat, I had plenty of software to play with, if not a surfeit of talent.
With the annoyance of having to produce so many sizes and aspect ratios for assets it's no wonder there are so many apps which seems to cater for very specific parts of the development process. Overall it's pretty affordable to have a set of tools which will cater to the process though. Apps like Acorn and Pixelmator are both pretty cheap at about US$30 each and then tools like Prepo are free.
Prepo is a cheap (free for the basic version, which does a lot) and cheerful image prep tool which will export images at the sizes required for 1x, 2x and 3x artwork within an app, and also launch icons, spotlight, app icons and so on. Ever so slightly unstable, but it's actually pretty good.
So that bit about stuff I check out being affordable? PaintCode 2 stretches that at AU$160ish in the Mac App Store (or US$99 from their website). It does do some really nice stuff for taking vector drawing tools and giving you either image files or Objective C/Swift code for Core Graphics calls. It's something I have barely scratched in terms of what it can do so far, but am looking forward to doing more with in the future.
I've posted about the Affinity apps before, but I used them a lot and really enjoy using them, particularly Designer. It does some really nice things with path merging and editing which is far more fiddly with Illustrator. I've done far more with Photoshop and Illustrator previously and haven't really gotten up to the level I'm capable of with Photoshop in particular, but I'm looking forward to getting there. Much more affordable than Adobe's stuff to boot.
I'm not a big fan of iMovie on the whole; it still doesn't do as much as I'd like when it comes to layers, editing titles and transitions. Its big plus is that it now has a preset for App Previews so doing up the previews for the App Store is as easy as firing up Quicktime Player, making a new movie recording and setting it to record your device's screen, and then dumping it into iMovie.
The downside of iMovie is it won't let you export App Previews into different resolutions. MPEGStreamClip will. Just whack your preview in, export as MP4 and you're away. In general, it's also a great clipping tool for movies. Also free.