Based on the title the first thing that popped in my mind was https://www.aseprite.org/ there source code is freely available to anyone https://github.com/aseprite/aseprite/ and if you search some more you can find how to install it at https://github.com/aseprite/aseprite/blob/master/INSTALL.md But none of these links are easy to find and the installation is not that simple either. Is this way of doing things good/bad? I just do not really know how to feel about it. It's partly better then not having the option available, but, i just don't know to feel about it.