Four things come to mind: * The AK-47. Love or hate guns, the AK was designed with tolerances that encouraged simultaneously good maintenance patterns and using it as a gorram hammer if the need came to it. * Nalgene bottles. Impact resistant, infinitely screen printable, polycarbonate body, cheap and everything you could want. * The venerable aluminum drinks can: The sheer amount of engineering that has gone into ma…
In addition to its linear descendants, it was widely copied and some of the copies where arguably better (the Isreali Galil, the Finn RK62, Vector R4).
One of the few guns to appear on national flags.
All of that said, for a professional army there are many better (where better is context dependent as most things are) service weapons but for "was a farmer, now an insurgent" use the AK has few equals.
Also for the pedantic, what most people think of as the AK47 is actually an AKM, the actual AK47 had a relatively (compared to its entirety) short service life, the Soviets started phasing them out in 1959.
The family of rifles has change remarkably from wood furniture in 7.62mm to modern polymers and 5.45mm and while they've rejigged the internals and changed things around an AK is immediately recognisable and you can see the AK47 in all of them.
The only other platform that I can think of that is remotely as adaptable is the AR-family.
I don't own guns, I think civilian ownership of guns is fine if very heavily regulated and with a purpose - even if that purpose is "I like shooting targets" (UK model of gun control) - I'm just fascinated by the history/engineering.