Linux is a clone of the Unix kernel, written from scratch by Linus Torvalds with assistance from a loosely-knit team of hackers across the Net. It aims towards POSIX and Single UNIX Specification compliance. It has all the features you would expect in a modern fully-fledged Unix kernel, including true multitasking, virtual memory, shared libraries, demand loading, shared copy-on-write executables, proper memory management, and TCP/IP networking.
Endian Firewall is an all-in-on Linux security distribution that turns any system into a full-featured security appliance. It features a stateful packet inspection firewall, application-level proxies for various protocols (HTTP, POP3, SMTP), anti-virus support, virus and spam filtering for email traffic (POP and SMTP), content filtering of Web traffic, and a "hassle free" VPN system based on OpenVPN.
Nuttx is a real-time embedded operating system (RTOS). It has a small footprint that is usable in micro-controller environments. It is fully scalable from tiny (8-bit) to moderate embedded (32-bit) systems. It also aims to be fully compliant to standards, to be fully real time, and to be totally open.
Slackware is the longest-running distribution of the Linux operating system. Slackware offers a stable and secure version of Linux that is perfect for home, office, or educational use. Slackware is easy for beginners to install, but contains all the advanced features required by the experienced UNIX power-user.
GeeXboX is a standalone media player Linux distribution, similar to MoviX. It's a small bootable CD that allows you to play your favorite video (DivX, XviD, H.264, MPEG 1/2, VCD, DVD, OggMedia, Windows Media, RealMedia, etc.) and audio (MP3, Audio CD, Ogg Vorbis, FLAC, MPC, etc.) files. It also supports networking, and is able to play media from Windows/Samba share, NFS, UPnP A/V Media Servers, RTP/RTSP servers, or SHOUTcast. It supports TV-out, TV tuners, DVB cards, and WiFi cards. It is based on MPlayer, and can be used on any x86, x86_64, or PowerPC computer. It's easy to modify the source to build your own GeeXboX or use an alternative boot method.
m23 is a software deployment system for Debian GNU/Linux that allows you to install and administrate hundreds of clients via network. It can partition and format clients and install Debian, (K/X)Ubuntu, Linux Mint, Fedora, OpenSuse, and CentOS operating systems on your virtual and physical clients. Group functions allow the comfortable update and installation of further packages during operation. Mass installation functions simplify your administration chores. m23 has a Web interface. Backup functions are implemented for server and clients.
Tor-ramdisk is a uClibc-based micro Linux distribution whose only purpose is to host a Tor server in an environment that maximizes security and privacy. Tor is a network of virtual tunnels that allows people and groups to improve their privacy and security on the Internet. Security is enhanced in tor-ramdisk by employing a monolithically compiled GRSEC/PAX patched kernel and hardened system tools. Privacy is enhanced by turning off logging at all levels so that even the Tor operator only has access to minimal information. Finally, since everything runs in ephemeral memory, no information survives a reboot, except for the Tor configuration file and the private RSA key, which may be exported and imported by FTP or SSH.
INSERT (the Inside Security Rescue Toolkit) aims to be a multi-functional, multi-purpose disaster recovery and network analysis system. It boots from a credit card-sized CD-ROM and is basically a stripped-down version of Knoppix. It features good hardware detection, fluxbox, emelfm, links-hacked, ssh, tcpdump, nmap, chntpwd, and much more. It provides full read-write support for NTFS partitions (using ntfs-3g), and the ClamAV virus scanner (including a fairly recent signature database and a GUI). It provides partition handling with gParted and also has a network boot facility.