I've been using NeoPaint and PSPX9 on Windows 10 and they both work great.
I've been using PSP since I was like 10, so I am most used to that one's interface.
Since I don't do a lot of actual graphics editing and mostly use it for palette diddling/cut/copy/etc., it does things I need.
ProMotion looks like it probably does good stuff for free, but the interface immediately makes me itchy. It's got this weird flat-look to it that drives me nuts and doesn't seem to have a way to make it not do that. Everyone's mileage may vary there. It might just be Windows 10's new GUI crap doing it.
I had to lol when I saw that "pixel perfect painting" was not part of the free package. Makes it sound like it f*cks your art up while you move the mouse around. It seems to do pixel jigglies fine though.
All of these options are better than Photoshop for PCE, btw.
Photoshop f*ckin inverts the damn PCX palettes, and screws life up, and causes earth to tip the wrong way, and people die.