
Slackware Linux is the world's oldest surviving Linux distribution. It wasn't the first Linux distro, that distinction belongs to the Softlanding Linux System (SLS), but Slackware has been going strong since its first release in 1993 and shows no signs of slowing down.
Slackware Linux is primarily developed and maintained by Patrick Volkerding, who founded the distribution in 1993. Volkerding uses a conservative approach to Slackware, sticking with the most stable versions of packages rather than going with cutting-edge software. For example, Slackware has been slow to adopt new versions of the Linux kernel as part of the default installation
Volkerding says his philosophy is to produce the most "UNIX-like" Linux distribution, with simplicity and stability being the most important considerations for the distribution.
Slackware was distributed by Walnut Creek CDROM until Wind River Systems purchased Walnut Creek (as part of the purchase of Berkeley Software Design, Inc. (BSDI). Slackware was "orphaned" by Wind River Systems. Slackware is now distributed by Slackware Linux through the Slackware Store.
Slackware does not have a set release cycle, but Slackware tends to have at least one release per year, and sometimes multiple point releases -- though generally no more frequently than two a year.
While most Linux distros offer live CDs and GUI installers, Slackware has stuck with the same tried and true menu-driven text mode installer for many years. While it's not a point-and-click affair that many users would be used to, it's still relatively user-friendly.
Slackware also uses its own packaging system, with software distributed in compressed tarballs and managed using Slackware's pkgtools utilities. Unlike many Linux distributions, Slackware's native tools do not provide dependency information or automatic handling of dependencies or package conflicts. An online guide to the Slackware installer is available.
The distribution was originally distributed on floppy disks, and the software was divided into software series. Slackware packages are still categorized by software series, even though the distro is now available on CDs. Only the first Slackware CD is needed for an install, but the additional CDs offer a wider selection of packages, as well as the extras, testing, and other packages.
As befits a distribution of Slackware's age, a number of Linux distributions use Slackware as a base to build on. For example, Zenwalk Linux is based on Slackware, with a focus on speed, multimedia and desktop applications, and simplicity. Unlike many distros, Zenwalk is streamlined to offer just one application per task, so users aren't confronted with several applications for Web browsing, mail, document editing, and so forth.
Zenwalk comes in two flavors -- a full installation with a complete set of desktop applications and developer libraries, and a server install without X and desktop applications for users who want to use Zenwalk as a server distro.
Vector Linux is a lightweight distro that uses Xfce and is based on Slackware. Vector comes in four editions: a live CD, the standard edition with Xfce, a small office/home office (SOHO) flavor based on KDE, and a "deluxe" edition that is only available via mail order.
Slackware doesn't offer an AMD64 port, but users with AMD64 machines can use Slamd64, an unofficial port of Slackware to AMD64 machines. Slamd64 is based on Slackware, but is compiled from source for AMD64 machines. It's also a multi-library system, meaning that it's possible to run 32-bit applications under Slamd64 without any special setup. This allows the use of applications, like Macromedia Flash, that aren't available in a native AMD64 version.
While not a distribution, specifically, you might want to check out dropline GNOME, if you prefer the GNOME desktop. The dropline team offers a set of Slackware packages for current GNOME releases and related applications, since Slackware no longer comes with GNOME.
If you'd like to try Slackware, head over to the Slackware site and pick a mirror closest to you, or try using one of the BitTorrent trackers. You should be able to get decent speeds from the Torrents even when it's been a while since a new release.