Slackware Linux, a complete 32-bit multitasking "UNIX-like" system that is currently based around the 3.2 Linux kernel series, has just reached the venerable age of 20.
It's not the easiest operating system to install and not exactly user friendly, by it has managed to survive a very long time and spawn numerous other distributions.
“The Slackware Linux distribution (v. 1.00) is now available for anonymous FTP. This is a complete installation system designed for systems with a 3.5" boot floppy. It has been tested extensively with a 386/IDE system.”
“The standard kernel included does not support SCSI, but if there's a great demand, I might be persuaded to compile a few custom kernels to put up for FTP,” reads the initial announcement posted by Patrick J. Volkerding back 1993, on July 16.
20 years later you can download Slackware 14.0 from Softpedia.