Krita is a free open source piece of Painting software. It's really nice... but it's a resource hog. I was using it as my primary art program before purchasing Affinity Photo and Affinity Design. The problem is this: Inside programs like Photoshop, Affinity products, and many others -- there's really not any tools for working in perspective. The only exception to the rule is Sketchbook Pro... but even their perspective tools pale in comparison to what you can do with Krita's Assistant tool (Of course, Sketchbook Pro's tools for perspective work a bit better, but they just aren't as versatile).
Now Affinity has the Perspective Warp, which is cool. If I wanted to draw each face to a building individually with a HEAD ON view, I can transform them into perspective. That's cool. But I know how to draw perspective, I don't need to cheat the workflow. I can work just as fast WITH REAL perspective drawing tools. And Fisheye perspective -- the sorts of perspective tools that you can make as seen in the book "Prospettiva ZeroSei Manuale di Prospettiva Lineare e Curvilinea" that would be a godsend. Sometimes I like drawing backgrounds for 2D animation, and being able to draw one image that's a full 360 degrees is awesome. (I teach a few ways of drawing like that on my youtube channel youtube.com/orphanlast).
Anyways -- Krita's Open Source. So, you can look at the code swipe it, improve it (and it does need some improvement), and Affinity can come out of it with NOT needing to do much R&D for this feature, having something that even the industry standard art program doesn't have and it'd be better than what ANY art program has done prior.
Just saying -- this could work out really well for Affinity photo