Inkscape 55
If The GIMP is the Linux answer to Photoshop, then Inkscape must be its answer to Illustrator. Inkscape is a powerful vector graphics editor, and it's perfect for producing slick, stylised graphics. It's especially suited to the web because its native format is SVG, an official web standard supported by the majority of today's browsers - in fact, there are over 30,000 Inkscape-produced files in the Wikimedia Commons. It's also ideal for making desktop icons that scale smoothly. Also available for Windows and Mac OS X.
Ardour 38
While it may surprise you, Linux is building a reputation in the music world thanks to Ardour, a feature-packed Digital Audio Workstation (DAW). Ardour lets you record and play as many tracks as your hardware can handle, with non-destructive editing and countless effects. It does lack MIDI sequencing support (that's coming in version 3), but if you're happy to work with audio directly, or use an external sequencer, Ardour is a fantastic way to make music. Platform: Linux, Mac OS X
Stellarium 41
If you've ever spotted something in the sky and wondered what you were looking at, Stellarium is for you. After you've told it where in the world you are, Stellarium gives you an accurate, interactive 3D map of the planets and stars, either for the current date and time, or any time in the past or future. You can easily zoom out to view the major constellations, or zoom in on Saturn's rings or the moons of Jupiter. Also, available for Windows and Mac OS X.
Rawstudio 46
With the rise of digital SLR cameras, more and more people are using RAW format, and Rawstudio is the easiest way to handle these files under Linux. It lets you open RAW files and perform preliminary processing on them, such as colour management, white balancing, exposure correction, cropping, and straightening, all in full RAW fidelity, before exporting them to JPEG or PNG for further editing. It also supports batch processing, so you can perform corrections across sets of photos with ease.
ytnef 43
They're the bane of our existence sometimes - those "winmail.dat" files that Outlook and Exchange users just can't seem to help sending sometimes, despite endless fiddling of their mail sending options. When you receive one and need to fetch the rich, chocolatey attachment hidden inside, ytnef is the tool you need. Just give it the name of the winmail.dat file to process to list its contents, or add the "-f" option to extract it.
Also see: 5 Free PC Apps You Can't Do Without