Six years ago tomorrow (yes really!) Valve announced the Steam for Linux beta for a limited amount of interested gamers. After getting more responses than they expected (over 60,000) they kept the testing pool quite small.
Later that month, on November 21st Valve added an additional 5,000 testers to help find more issues. Rather quickly, Valve pushed the beta out for a much larger audience on December 19th in that same year with anyone being able to try it. I remember it extremely well, having a rather ordinary week and suddenly being thrown into the thick of it making sure I could test everything possible.