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!
Adobe Photoshop - Adobe Photoshop is a webtop application for editing images and photos online.
FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.
Krita - Krita is a professional FREE and open source painting program. It is made by artists that want to seaffordable art tools for everyone. Concept art. texture and matte painters, illustrations and comics.