Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
Scrivener - Scrivener is a content-generation tool for composing and structuring documents.
Sketch - Professional digital design for Mac.
Celtx - Celtx is a scriptwriting software platform with applications in a wide range of mediums but that specializes in helping screenwriters.
Affinity Designer - Professional creative software, exclusively for Mac.
Trelby - The free, multiplatform, feature-rich screenwriting program!