Best free photo editors

Hi there! The photo editors I'm going to show you are my favourites and I use them all the time. The ones to your computer works good with Linux (Ubuntu) since that's what my own computer is. I've tried all things out for myself and if it says it also work on Windows I've tried it there too, as for Mac/iOS I haven't tried it out for myself. If it says it will work on Mac/iOS I wrote it out after doing a bit of research but never tried myself because I don't have any Apple devices. I hope you find this helpful!

Pixlr

Form: App (Android/iOS), software (Windows/Mac), web apps (you can access all webb apps in Chrome, in Mozilla you can't use Pixlr Touch up)
Website: https://pixlr.com/
Positive:
+ Pixlr is simple to use but you can still do a lot of things with it.
+ I love the idea that you can use it online, on your phone or on your computer.
+ None of the different versions have given me any problems, everything works fine. Most of the time I use the web app Pixlr Express. If I have time I also like to go through the web app Pixlr Touch up.
+ You don't have to sign up to use the web app unless you would like to.
Negative:
-  In Express you have the ability to make a collage if you want but every time I use this feature I find that the quality of my pictures don't end up very good. If I save the highest possible quality I still don't find that my photos look that good after being saved.
-  I don't like that it's software isn't compatible with Ubuntu but maybe it'll come in the future.
-  In order to use the app/web app you need to be online.

PicMonkey

Form: Web app (all browsers)
Website: http://www.picmonkey.com/
Positive:
+ It's super good to make collages with.
+ You can easily choose seize, shape, colours and so much more.
+ It's not needed to sign up and you can do a lot of things.
+ You can use this to edit, touch up or make some kind of banner with your own photos.
+ If you just want to play around you could also just start with one of the photos they provide.
Negative:
-  Not everything is free.
-  If you would like to be able to use all features they have you have to be a Royale member. They give you a first free month but after that you will have to pay in order to continue your Royale membership.
- Because it's a web app you will need to be online in order to be able to edit and save.

Gimp

Form: Software (works with everything)
Website: http://www.gimp.org/
Positive:
+ You can do whatever you would like to do.
+ It's more advanced than the previous two and I feel like it's all of Pixlr's different web apps combined in one.
+ It doesn't matter if you have Windows/Mac/Ubuntu or anything other because of the information I could find online everyone can use it.
+ You can download packs with brushes and things like that that adds on to your software.
+ Because it's a software you can also edit when you are offline as well.
Negative:
-  I wouldn't recommend to complete beginners if they just want to edit a photo fast. It can take some time to get used to the program and the best way to get to know it is by just simply playing around with all different settings you find but that can take some time.

BeautyPlus - Magical Camera

Form: App (Android/iOS)
Website: None
Rating: 4,3 stars in Google Play
Positive:
+ It's very easy to handle.
+ You have a lot of different things you can do to your photo like different filters, lighten skin, remove pimples etc.
+ Good results and it doesn't take very long.
Negative:
- This app is for selfies/portraits and I don't think it would work very well on something else, except for filters maybe.
- You need to be online to use the app.