When was the last time when serious new instrument was invented ?

Well... have you already seen/heard every instrument in this world? Why are you looking for new instruments? Go east, to the continent of Asia (especially) and you will find instruments (you’ve never heard of) that will blow your mind for many lifetimes...

Well, what makes you think we are not familiar with Middle Eastern, Indian and others instruments ? None of those by themselves exactly blow my mind.

The overall most impressive instrument is still human voice followed by, I think, piano.

I like Moog synthesizers a lot, by the way.

Tom Waits has some pretty strange instruments in his music at times. Not sure if it’s anything new though. 
 

Basically, I had nothing material to contribute, just felt the need to interact! 
 

Hope you all have a good Sunday evening!

The wish to interact is very 'material', that's, substantial.

I will take a look at Tom Waits' arrangements.

The Therman and the Melotron come to mind as newer instruments.