In addition to the default application, Photos, I have the ones in the image above and another, namely Snapseed - if I do not consider Instagram. So, from left to right:
LightMeter - is a useful application for anything other than photography with the phone. I downloaded it for the relatively few moments when I shoot the movie manually. But, as my film camera also has a diaphragm priority mode, I open it from Easter to Easter
Sunrays - is an application that I also use from Easter to Easter, but it is very useful when you want to schedule an outdoor photo shoot. It's based on Google Maps and shows you how the sun shines depending on where you want to take pictures. I think I've written about her before. The idea is that the lunch sun is horrible for portraits - and not only - because it burns, you have strong shadows, etc. This application shows you the position of the sun depending on, for example, the building you want to pose and shows you the hours (obviously, the green range is preferable) in which you have the right light.
SKRWT - from "Screw it" - is an application for perspective correction. It helps you to have vertical and horizontal verticals. I have an obsession with verticals, so I use it occasionally when Snapseed doesn't seem like enough
Instasize - as the name suggests, is a landscape or portrait picture in a square - that is, it adds a white, black background, etc. around the image. Meanwhile, Instagram allowed images to be uploaded without the need to crop them.
Manual - is an application that allows you to change settings. It's not completely manual, because you can't change the aperture on your mobile, but you can control the ISO and the shutter speed. In addition, the function I like the most is the level one, just so I don't waste time with too many perspective corrections.
Lightroom CC - is the mobile version of the Adobe application. It's free, it has almost all the main functions in the desktop version, the export quality is the right one. It's counterintuitive in places, but it's useful. I use it when I'm not happy with what Snapseed offers me
Snapseed is a separate chapter, that's because I ended up using it as the main editing application for the functions it incorporates. It has two versions, depending on how generous the phone's display is (on the iPhone 5s it looks different from the iPhone 7 or 7s).
It is super easy to use, it is very intuitive, the export quality (the final picture, the one saved in the phone, that is) is decent, it has white balance correction, perspective correction and basic corrections, from brightness and contrast to Sharpening and Clarity (well, Google calls it Structure, just like in Instagram - I might hit the ground running, but I don't see any difference between the two).
And that's about it. Of note, three of them (Instasize, Lightroom and Snapseed) also have filters for those who are passionate about them. I don't use it, I prefer to let the image be seen as close as possible to what it really looks like and I don't put my nose away from the basic corrections.
I don't put links to them anymore, because it doesn't make sense, you can find them all in the AppStore