rather depends on where they are used......
as a general lub I use "D" Synthectic motor oil......so thats bed ways and sliders on metal working machinery....and the auto lube system on my Bridgeport mill.....
totaly enclosed gearboxes as in metal lathes I use the red automatic trans oil......does the lub, no real drag and dosen't froth...
(that white Merc Sprinter that comes poast you on the motorway carrying a ton at 100MPH uses the same oil, so good enough for me)....there are fancy oils made by leading makers for all of the above but can be around £40 per liter or more....
as for metal working suds (milky looking coolant) when my 5 gal tube of soluble oil is finished all my metal machines will get 46 grade Hydraulic oil as coolant.....
the back gears on metal lathes get Chains saw blade oil because it's very sticky (long grain molecules) so it doesn't fly off, just a few drops every once in a while......
Now wood working machines, the raise and lower quadrants plus on some tilt gears need a dry lube on the teeth them selves but often the shaft in the casting has an oil dropper or hole......powdered Graphite is one, same as used on car door locks....u cant use a wet lube because it atracts wood dust.....painted on or mostley now in an spray can.....
High speed spindles are either lubed with oil or grease....my Wadkin P/T had oil drippers.....they got a few drops of oil before start up and then every hour after that.....
there's a lot of talk about modern gearbox oils eating Phosfer Bronze bushings.....I have never come across this in my working life but if you use 80-90W Synthetic it makes no difference now.....
I got fed up with a cupboard full of weird oils n greases, all getting dusty and fluffy.....besides I was moving so need to simplify all these oils......so now have been using the above for years with no problems....
Some of my machines are brand new Myford S7 lathe and the Myford milling machine.....these look just as they did when out of the box....if I thought what I was doing would wreck them I'd stop as I have a lot of money invested in them....
hope that helps a bit.....but lube is a sacrosanct subject for most....all my machine work for a living.....