PhotoScape

Photoscape is a fun and easy photo editing software that enables you to fix and enhance photos.

Source from http://www.photoscape.org/ps/main/index.php

Irfan View

IrfanView is a very fast, small, compact and innovative FREEWARE (for non-commercial use) graphic viewer for Windows 9x, ME, NT, 2000, XP, 2003 , 2008, Vista, Windows 7, Windows 8.

It is designed to be simple for beginners and powerful for professionals.

IrfanView seeks to create unique, new and interesting features, unlike some other graphic viewers, whose whole "creativity" is based on feature cloning, stealing of ideas and whole dialogs from ACDSee and/or IrfanView! (for example: XnView has been stealing/cloning features and whole dialogs from IrfanView, for 10+ years).

IrfanView was the first Windows graphic viewer WORLDWIDE with Multiple (animated) GIF support.
One of the first graphic viewers WORLDWIDE with Multipage TIF support.
The first graphic viewer WORLDWIDE with Multiple ICO support.

Source from http://www.irfanview.com/main_what_is_engl.htm

Paint.NET

Paint.NET is free image and photo editing software for computers that run Windows. It features an intuitive and innovative user interface with support for layers, unlimited undo, special effects, and a wide variety of useful and powerful tools. An active and growing online community provides friendly help, tutorials, and plugins.

Source from http://www.getpaint.net

Photo Pos Pro

Photo Pos Pro is a free photo editing software offers users a wide variety of possibilities in the fields of Image Enhancing and Image Editing and in the field of Computer Graphics Design. Using the editor you can perform various tasks, from simple basic tasks to complex tasks; you can edit existing images, create new works based on existing images, create new works from scratch and more.

Source from http://www.photopos.com/Photo-Pos-Pro-Free-Photo-Editor.asp

GIMP

GIMP is a multi-platform photo manipulation tool. GIMP is an acronym for GNU Image Manipulation Program. The GIMP is suitable for a variety of image manipulation tasks, including photo retouching, image composition, and image construction.

GIMP has many capabilities. It can be used as a simple paint program, an expert quality photo retouching program, an online batch processing system, a mass production image renderer, an image format converter, etc.

GIMP is expandable and extensible. It is designed to be augmented with plug-ins and extensions to do just about anything. The advanced scripting interface allows everything from the simplest task to the most complex image manipulation procedures to be easily scripted.

One of The GIMP's strengths is its free availability from many sources for many operating systems. Most GNU/Linux distributions include The GIMP as a standard application. The GIMP is also available for other operating systems such as Microsoft Windows™ or Apple's Mac OS X™ (Darwin). The GIMP is a Free Software application covered by the General Public License [GPL]. The GPL provides users with the freedom to access and alter the source code that makes up computer programs. 

Souce from http://docs.gimp.org/2.8/en/introduction.html#introduction-gimp

Fast Stone Image Viewer

FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor. It has a nice array of features that include image viewing, management, comparison, red-eye removal, emailing, resizing, cropping, retouching and color adjustments. Its innovative but intuitive full-screen mode provides quick access to EXIF information, thumbnail browser and major functionalities via hidden toolbars that pop up when your mouse touches the four edges of the screen. Other features include a high quality magnifier and a musical slideshow with 150+ transitional effects, as well as lossless JPEG transitions, drop shadow effects, image annotation, scanner support, histogram and much more. It supports all major graphic formats (BMP, JPEG, JPEG 2000, animated GIF, PNG, PCX, PSD, EPS, TIFF, WMF, ICO and TGA) and popular digital camera RAW formats (CRW, CR2, NEF, PEF, RAF, MRW, ORF, SRF, ARW, SR2, RW2 and DNG).

Source from http://www.faststone.org/FSViewerDetail.htm