Image: http://www.flickr.com/photos/frenchy/ (Creative Commons)

One of the benefits of open source software that many people are most familiar with is that it's free to download. This means you can grab great applications — such as Mozilla's Firefox Web browser, the OpenOffice.org office suite or the GIMP photo editing program — without paying a cent. However, the other major benefit of truly open source software (some "open source" software licences are more restrictive than others) is that you're allowed to modify a program and redistribute your altered version so other people can enjoy it.

Linux is a classic example of this: there are hundreds (at least!) of different Linux-based operating systems. Most people will be familiar with some of the big names — distributions like Ubuntu, Red Hat Enterprise Linux, Debian and Mandriva. Most of the well-known Linux distros are designed to be used as general purpose desktop operating systems or installed on servers. But beyond these distros are hundreds of others either designed to appeal to very specific audiences or to fulfil the somewhat niche needs of some users. We rounded up some of the most interesting Linux distros out there that you might not have heard of.

Insecure by design: Damn Vulnerable Linux

Damn Vulnerable Linux is "The most vulnerable and exploitable operating system ever" according to its Web site. It's designed for security training; it includes training material and exercises (as well as a whole bunch of flaws to exploit). As Mayank Sharma notes: "Damn Vulnerable Linux (DVL) is everything a good Linux distribution isn't. Its developers have spent hours stuffing it with broken, ill-configured, outdated, and exploitable software that makes it vulnerable to attacks."

Indulge in paranoia: Tinfoil Hat Linux

Image: Tinfoilhat.shmoo.com

Tinfoil Hat Linux is pretty much the opposite of Damn Vulnerable Linux: it's designed for the paranoid among us.

"It started as a secure, single floppy, bootable Linux distribution for storing PGP keys and then encrypting, signing and wiping files. At some point it became an exercise in over-engineering." According to its developers, a possible reason for using it is that that "Illuminati are watching your computer, and you need to use morse code to blink out your PGP messages on the numlock key." They're joking. Probably. (In case you want more tinfoil protection, there are some links to a site about aluminium foil deflector beanies and tinfoil suits.)

CSI Linux: CAINE

CAINE (Computer Aided INvestigative Environment) is probably one of the coolest niche Linux distributions around. It's designed for digital forensics (so sadly, no blood spatter analysis) and was developed at the Information Engineering Department of the University of Modena e Reggio Emilia in Italy. It includes software such as TheSleuthKit and Autopsy Forensic Browser for examining file systems, data recovery applications, steganography tools and utilities for securely wiping drives (you know, in case someone else has a copy of CAINE).

Open source engineering: CAELinux

Image: Caelinux.com

CAELinux is designed for computer-aided engineering (CAE). It's an Ubuntu-based operating system that's packaged with a range of open source applications designed for simulating physics involving "non-linear thermo-mechanics, coupled fluid-structure dynamics, seismic / non-linear explicit dynamics, contacts, visco-plasticity, fluid dynamics, heat exchange, convection heat transfer and radiation, electro-magnetics".

Seeking open source converts: Ubuntu Christian Edition

Image: Ubuntuce.com

According to the project's FAQ page, Ubuntu Christian Edition is not intended to split the Ubuntu community. Instead, it's "intended to draw a larger Christian base to the already thriving community of Ubuntu users. The Ubuntu Christian Edition simply makes it easier for Christians who are new to Linux to see the power of Ubuntu combined with the added benefit of having the best available Linux Christian software pre-installed". It's a good example of a community constructing a Linux OS to meet their needs. It includes applications such as Xiphos and e-Sword (Bible-study tools), as well as DansGuardian Web filtering software.

Frag-tastic: live.linuX-gamers.net

Image: live.linux-gamers.net

The live.linuX-gamers.net distro is a great piece of Linux evangelism: it's a live DVD (you don't need to install it on your hard drive) and it does exactly what it says on the box (err, or downloadable ISO file, or something). It's designed to showcase Linux as a gaming environment, and ditches all the standard productivity software included in distros in favour of open source games.

Hard disk wizardry: Parted Magic

Image: Partedmagic.com

Parted Magic is a one-stop shop for manipulating your PC's hard drive — creating and manipulating partitions (if you want to dual boot operating systems, for example), benchmarking drive speeds and testing for bad sectors.

Get creative: Musix GNU+Linux

Image: Musix.org.ar

There are a number of Linux-based operating systems designed for multimedia work. Musix is one such distro, and it's a based on Debian. It has the distinction of being on the Free Software Foundations list of fully free (as in speech) Linux distros. Musix GNU+Linux is available for download as a live CD/DVD.