Recently I received a list of numerous household cleaning/repair tasks that WD-40 can be used for.
That message reminded me of how the first time I used WD-40, it smelled exactly like the waxy cloths we used in 1961 to wipe down and clean the stainless steel walk-up window counters at McDonalds. And after reading the list (but see below). I would not be at all surprised to learn that WD-40 was (and still is) used in many places to clean and protect stainless steel counters and other products.
However, some of the uses claimed in that message for WD-40 made me a bit suspicious. For example, I cannot imagine spraying WD-40 on a chalkboard (do chalkboards even exist anymore?) to clean it -- wouldn't the waxy spray make it much harder to write with the chalk? If anyone has actually tried this, please let me know the outcome.
Anyway, I Snoped the list from that message. Indeed some of the uses of WD-40 are not necessarily recommended by the manufacturer. They might or might not work, but the manufacturer won't go on record supporting them. To see the email listing all the miraculous uses of WD-40, along with the manufacturer's amendment of that list of recommendations, see this.
Also, according to Snopes, no, WD-40 is not made of fish oil. But yes, it does stand for the fortieth attempt to devise a water-displacing lubricant.