potrace - Open source program that transforms bitmaps into vector graphics.
Icons8 Background Remover - Quickly remove the background from any photo
Vectorizer.io - Fast and easy way to vectorize an image online
ClippingMagic.com - Remove image backgrounds online. Make backgrounds transparent, white, etc. Edit, crop, rotate, fix colors, add shadows, all you need for great photos!
Autotracer.org - Free online image vectorizer
Trace by Sticker Mule - Remove the background from any image for free