Toolabs DSM - Design System Manager plugin for creating themeable designs
Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
Evie by unDraw - MIT licensed illustrations for your next project
Sketch - Professional digital design for Mac.
Haiku - Haiku is an open source OS catered specifically to the needs of personal computing.
Affinity Designer - Professional creative software, exclusively for Mac.