Well, everyone has their own workflow for creating art, i go Blender for 3d models and photoshop for textures, Gimp can be a good subtitute for it; but im way too used to photoshop by now.

As for engines BGE has not good popularity, either try Unity3d (not Foss) which is very easy to get in, or go for Godot which is developing really well and is fully open.

Just have a look at all of them and chooe the one you like the most, also, there are many more out there, but this ones are the most famous.

GIMP mostly, because that is what I learned computer art on anyway.  I have never even used photoshop.  I was supposed to be an electrical engineer, but I never passed the math.  Once I played around with GIMP, I couldn't really stop myself from making art with it since it was such an upgrade from ms paint.

I use Photoshop really for pixel art and texture editing though ill create the base for textures in Autodesk Maya. I have Aseprite but I dont use it much as of right now, but ill probably get into it when I begin doing more heavily animated pixel art. I use Autodesk Maya for all of my 3D work since thats what im trained in, however I keep Blender on the side just incase someone wants something done in it for whatever reason.

I tried using GIMP for pixel art, but it's really clumsy. After struggling for a while with Piskel, I ended up working with mtPaint. It's quirky, but very lightweight, and designed for this sort of thing outright. Neither can replace Inkscape though; they're made for different kinds of graphic altogether, depending on what you need for any given game.

I've been compiling and curating a list of (mostly) free software (and resources) here:-

http://www.violationentertainment.com/wiki/tiki-index.php?page=Free

I still have a pretty huge amount of stuff to test, but I'm determined to keep the list growing and weed out the 404s, and make mirrors of lost software if need be.

@shirish Do you mean GIMP 2.10?
There was no huge shift in UI from 2.7 to 2.8 or even 2.8 to 2.10 (comparing it to something like Blender 2.4 to 2.5).
Indexed mode is a step up from 2.8 but there's still a lot holding it back, so I'm not all in it but it's what I use to pixel.

re general art:
If for some reason you're talking an artist in the big name industry, usually the only FOSS you'll see is under the hood (plugins, formats, etc.) or the OS. But I won't kid myself.

What little guys mostly use has been covered.
Blender or forks (BForArtists is a good one). There was Wings3D, but haven't heard much from this one lately.
2D is mostly GIMP or Krita.

@LDAsh Another great list. OGA needs to have a list like this stickied right up in your face in the forums.
Would be happy to help you out if you need tags or recommendation, I wanna collect this software too. Already found a couple other user-made lists.

Anyone is welcome to copy+paste from that thread, if they'd like, but I tried to keep it to stuff that is "legacy-friendly" (now moreso Win7) and no browser-only stuff, so there's plenty more that could be added.

I dont think Im an artist myself, at least not yet, but I love and use Aseprite.