The best one imo is Iudesk Photo Editor. Not good for drawing, but otherwise it has almost everything, ad-free version is just a few €$£ and minimum tracking compared to the big guns.

Open source options are lacking: Litrato, Pocket Paint and Simple Draw, each does something but still not much together.

• For phone: Snapseed (Google) but apparently it doesn't get updates anymore.
• For tablet: Krita. It also kinda works on a phone if you need it (like me). If you increase "Smallest width" in the developer settings you can make it more usable but the buttons will be really small.

I don't understand how mobile apps are still so limited compared to their desktop counter parts. Like I couldn't even find a single browser that has any of the dev tools in any normal desktop browser. Especially infuriating since websites can just willynilly disable features like downloading images.

Photopea is an online photo editor

Pocket paint

I don't know about open source, but the only Android app that comes anywhere close to the functionality of GIMP/Krita/Photoshop is Infinite Painter, AFAIK.

I generally edit my photos with photoshop but if I must do it with my phone I'm going to use Snapseed

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