digiKam - Professional Photo Management with the Power of Open Source
GIMP - GIMP is a multiplatform photo manipulation tool.
XnView MP - XnView is a free software that allows you to view, resize and edit your images. It supports more than 500 different formats!
Fiji - Fiji: A batteries-included distribution of ImageJ.
ACDSee Photo Studio - ACDSee becomes ACDSee Photo Studio — ACDSee Photo Studio Standard 2018 continues the ACDSee legacy
Adobe Photoshop - Adobe Photoshop is a webtop application for editing images and photos online.