GIMP - GIMP is a multiplatform photo manipulation tool.
remove.bg - Remove the background of any image 100% automatically
Pixlr - Pixlr® makes it easy to transform everyday images into stunning works of art.
ClippingMagic.com - Remove image backgrounds online. Make backgrounds transparent, white, etc. Edit, crop, rotate, fix colors, add shadows, all you need for great photos!
Photoscape - high quality photo editing software, that enables you to fix and enhance photos.
Bg Eraser - Background Eraser on Mac and Windows.