It's historic and unmaintained, and no website even exists, but I stumbled across this little gem of information regarding a distribution known as:
MCC Interim Linux
It was first released to the public in February 1992 by Owen Le Blanc, nearly a full year before Patrick first released Slackware in July 1993 and just months before Peter MacDonald released Softlanding Linux System in May 1992. However an anonymous FTP by MCC made Linux first available in November of 1991.
The only evidence of anything older was the legendary H. J. Lu's infamous Boot-Root floppy disks.
That's just awesome to have found that while doing a random drive through of Wikipedia.