SLS

SLS, variously known as the Soft Landing System or the Softlanding Linux System was either the first or the second Linux distribution, along with MCC (the Manchester Computing Center distribution). Both were created in 1992.

Slackware (1993) was initially intended as an effort to debug SLS that went a bit beyond that. Slackware is the oldest currently maintained distro, as both SLS and MCC have ceased activity.