3-in-One (original formulation) contains pale spindle oil, a small amount of corrosion inhibitor and a vegetable based component, citronella oil (ever notice the way 3-in-One smells?). While the original product remains available, these days the company also makes several other lubrications like "3-in-One Motor Oil", "3-in-One Professional Lubricant Spray with PTFE", and also the WD-40 family of products.
Indeed. "Pale spindle oil" sounds a bit mysterious, but the CAS number is the same as the heavy naphthenic oil specified in the current MSDS sheet. Citronella is probably still used, although it seems to be there simply as an aromatic component, as it's added in very small quantity. "Corrosion inhibitor" isn't even specified, described simply as a proprietary ingredient. However, even that is in very small proportion to the oil.
That it was marketed as "a lubricant, a rust preventative and a cleaner" is interesting. Though it should be remembered that pretty much any unadulterated mineral oil will do those things as well.
It is interesting that bicyclists have had some input on the
wikipedia entry, evidenced by the unsubstantiated claim, "It remains a popular lubricant for bicycle chains,
although it attracts more dirt than some modern alternatives and can be washed away by very heavy rain." As if it has some magical dust attracting qualities and is especially soluble in rainwater.