These free and open source applications for Windows, Linux, and Mac desktops put power into the hands of users without taking from their wallets.
This spectacular program comes closer than any other to replacing Photoshop for the casual user. It's neither cross-platform (it's Windows-only) nor open source (although it is free for use). But it's far more elegantly presented and immediately useful than its open source counterpart, GIMP. Layered editing, a gallery of plug-ins, tons of built-in effects (even some GPU-accelerated ones), and support for just about every major image format make this program well worth having. Paint.NET has some weaknesses - namely, text handling is awkward, and there's no way to create non-destructive manipulation à la Photoshop's adjustment layers. Both of those are being worked on for future editions of the program, though.
Free software's answer to Adobe Illustrator, Inkscape is polished, powerful, and loaded with tools that don't require a lot of guesswork to use well. Its native file format is conventional XML, and it can import and export from a whole bevy of existing vector and raster formats, as well as PDFs. The most recent version, 0.48, adds multipath editing, improved text handling, an interesting "spray" tool, and broad support for ICC colour throughout the program.
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