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.
Recovery Is Possible (RIP) is a CD or USB boot/rescue/backup/maintenance system. It has support for many filesystem types (Reiserfs, Btrfs, Ext2/3/4, HFS+, ISO-9660, Squashfs, UDF, XFS, JFS, UFS2, CIFS, MS DOS, NTFS, and VFAT) and contains several utilities for system recovery. It also has IDE/SCSI/SATA, RAID, LVM2, and Ethernet/Wireless network support.
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.
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.
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.
CentOS is an enterprise Linux distribution based on the sources from Red Hat Enterprise Linux. CentOS conforms with Red Hat's redistribution policy and aims to be 100% binary compatible. Each CentOS version is supported for 7 years (by means of security updates). A new CentOS version is released every 2 years and each CentOS version is regularly updated (every 6 months) to support newer hardware. Currently, there are 4 different supported CentOS releases: CentOS-5 is based on Red Hat Enterprise Linux 5, CentOS-4 is based on RHEL4, CentOS-3 is based on RHEL3, and CentOS-2 is based on RHAS2.1.