Most people keep throwing around the misconception that the Ukulele was engineered in all its (small) glory in the US.
The Ukulele spawned from the adaptation of the Portuguese instrument "Machete" (brought to the island by portuguese immigrants), which, in itself, is an adaptation/transformation of the Original, the "cavaquinho". If you look at it, it's mostly the same instrument, but with nylon strings...
You can read about both instruments on wikipedia (https://en.wikipedia.org/wiki/Cavaquinho / https://en.wikipedia.org/wiki/Ukulele), both articles are pretty correct.
I can attest to the veracity of the article on the "cavaquinho", since my birth city is where the instrument was engineered (along with a more guitar like, "roots" guitar, the "braguesa" - https://en.wikipedia.org/wiki/Viola_braguesa).
Both instruments (the cavaquinho and braguesa) are traditionally used in folklore music, but with some more experimental musical acts using them as centre pieces of their music or to add texture to their sound. You can read more on them on the portuguese articles of those pages, just use google translate, the information in the english articles is very basic.
As to instruments, that are clearly of Northern American origin, I would say the already mentioned banjo, but I didn't know that the bass originated there (well, given that the electric guitar as we know it, is, most likely an American invention, it only makes sense).