Yes, WD-40 was originally developed as a water displacement product - not for the retail market, but for the aerospace industry.
In the late 1950s a team of three employees of the Rocket Chemical Company in San Diego, California, led by chemist Norm Larsen were looking for a water displacement solution for NASA to protect the Atlas Space Missile from rust and corrosion. It took forty attempts to get the formula right, which is how the product found its name, WD-40 - Water Displacement 40th formula.
It was first retailed in 1958 in aerosol cans. Over the years, it's tended to be seen as a 'toolkit in a can', and along with a roll of duct tape can solve just about and fault or breakdown, except of course that it can't. Like many on the forum, I'd never let it near a vintage radio, but in fairness to those that do, the claimed uses on the can are stated as:
Stops squeaks
Drives out moisture
Cleans and protects
Loosens rusty parts ["Thoroughly penetrates and loosens seized parts"]
Frees sticky mechanisms.
I'm sure that most of us have used it for all of those purposes over time, the least satisfactory of which is as a penetrating fluid. Penetrating oil needs low surface tension, (EG: 'Plus Gas') the opposite quality from a water displacement product. If it's used on moving parts, (ball races in tuning caps for example), over time WD40 dries to a sticky residue.
I think that the company tacitly realised the limitations, and hence, some years ago now, they developed a range of nine specialist products, but for almost six decades the original WD40 has become so embedded in people's minds as a cure all, that the Specialist range hasn't become widely available. Most of us will have at least one can of WD40 but few will have any of these. The company has to be careful how they market the range, because the more they stress the special benefits of each one, by implication, the more they emphasise the limitations of the original everyday WD40:
Dry PTFE
De-Greaser
Contact Cleaner
Penetrant
PFFE lubricant
Silicone
White Lithium
Spray Grease
Cutting Oil
I use the dry PTFE on such things as curtain tracks, for which it's superb.
I've also got some contact cleaner, but have a can of De-Oxit, which will probably see me out.
For degreasing, I use brake cleaner spray, which really shits oil and dirt, then quickly evaporates leaving no residue.
About the only thing I use WD40 for is on my lathes, pillar drill and bandsaw to stop rust in my workshop in the winter months.
WD40 introduced the 'Smartstraw' some time back, which is a real boon as the little red straws always seem to go AWOL.
You can leave the straw down and just use the spray, or pull the straw up to direct it where you want it. Well worth the extra cost.
If you go to this link you can click on any of the 'cans' to find out more about the product:
https://wd40.co.uk/wd-40-specialist/
Some history about the company:
https://wd40.co.uk/about-wd-40/
Other brands and products are available!