Softlanding Linux System (SLS) was an early Linux distribution, founded by Peter MacDonald in mid-1992. It was the first to offer a bootstrap install disk from floppy, cdrom, network, etc. It was also the first comprehensive Linux distribution, containing more than the Linux Kernel and basic utilities, plus early GNU/Linux features such as the X Window System and TCP/IP.
SLS was probably the most popular Linux distribution at the time, and dominated the market until the developers made a decision to change the executable format that was not well received by the user base (a.out to ELF). During this time, Patrick Volkerding decided to modify SLS by tweaking and cleaned it up. He called his finished work Slackware. With the unpopular direction SLS had taken, Slackware quickly replaced it and became the dominant distribution used by nearly everyone.
Similarly Ian Murdock frustration with SLS lead him to create the Debian project.