DIGITAL IMAGING
Gimp
Also known as the GNU Image Manipulation Program, Gimp is a popular open-source software that is a credible alternative to Adobe Photoshop.
Provide a full suite of painting tools, such as brush, pencil and air brush, plus photo enhancement options, including the ability to fix perspective distortion caused by lens tilt.
More Photoshop-like features, such as Unsharp Mask and Watermark, plug-ins are available at the Gimp Plug-in registry at registry.gimp.org.
Photoscape
www.photoscape.org
This image editor features a variety of fun and easy-to-use tools that will help you spruce up your vacation photos.
Able to combine multiple snapshots into a photo montage and create animated GIF images using multiple images. A face-search tool allows to search for similar faces on the Web based on your portraits.
Paint.NET
www.getpaint.net
For doing basic cropping and re-sizing with some special effects and layers.