Multipaint 2020.2 by Tero Heikkinen AKA Dr. TerrorZ is an absolutely amazing graphics tool for Windows, Linux & Mac.  As described by the author:

With Multipaint, you can draw pictures with the color limitations of some typical 8-bit computer platforms. The screen formats supported are Commodore 64 high resolution, Commodore 64 multicolor, Commodore Plus/4 Hires, Commodore Plus/4 multicolor, ZX Spectrum, ZX ULAplus, MSX 1, Amstrad CPC mode 0/1 (and 0 with Overscan), Sinclair QL and Atari ST low resolution.

Please visit http://multipaint.kameli.net for the latest version and news.