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

Just remembered,

The Harmonium was another newer instrument.

How long ago was the kazoo invented?  

The cowbell is an idiophone hand percussion instrument used in various styles of music, such as Latin and rock. It is named after the similar bell used by herdsmen to keep track of the whereabouts of cows. The instrument initially and traditionally has been metallic; however, contemporarily, some variants are made of synthetic materials.

All kinds of unique and interesting Eurorack modules coming out weekly.

Every new pipe organ is unique.