Milton is a free and open-source, inifinte canvas paint program.
With Milton, you can paint with (almost) infinite detail. It feels raster-based but it works with vectors.
It is not an image editor. It is not a vector graphics editor. It is a program that lets you draw, sketch and paint.
There is no save button, your work is persistent with unlimited undo.
Download the latest release here: https://github.com/serge-rgb/milton/releases/