Depends with what you might want to achieve, some people will say inkscape or gimp. In my minimal experience while they win in some departments like plugins and features their UX and UI is really not as good, but that’s just how it worked for me, some people would swear by them.
What is the open alternative?
There sadly isn’t a viable one at the same level of functionality.
Edit: some random other comment appeared here. Fixed.
Depends with what you might want to achieve, some people will say inkscape or gimp. In my minimal experience while they win in some departments like plugins and features their UX and UI is really not as good, but that’s just how it worked for me, some people would swear by them.