Many of the following programs can be used as an alternative to Adobe Illustrator (a popular vector graphics editor).

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Autodesk Graphic (formally “iDraw”), Mac OS X (App Store), $30
https://itunes.apple.com/app/id404705039

Inkscape, Windows, Mac OS X, and Linux, free
https://www.inkscape.org/

CorelDRAW, Windows, $500
http://www.corel.com/corel/product/index.jsp?pid=prod5190074

Affinity Designer, Windows and Mac OS X (10.7+), $50
https://affinity.serif.com/en-us/designer/

Creative Docs .NET, Windows, free
http://www.virtualpen.com/

Alchemy, Windows, Mac OS X, and Linux, free
http://al.chemy.org/

Sketch, Mac OS X 10.10+, $100 (educational price: $50)
https://www.sketchapp.com/

Xara Photo & Graphic Designer, Windows, $90
https://www.xara.com/us/photo-graphic-designer/

Skencil, Linux, free
http://www.skencil.org/

Xara Xtreme, Linux, free
http://www.xaraxtreme.org/