Le Sacre du Printemps (The Rite of Spring), 1913, by Igor Stravinsky. The orchestral score is transcribed for two pianos here. Note the changing meter:

What instruments do you recognize, even if you can’t see them?

The ballet, performed with the original choreography by Vaslav Nijinksy:

Another score by a modernist Eastern European composer, based on Slovak folk music, which changes meters:

Which sounds like this:

This American folk song also has mixed meters, shifting between 2/4 and 5/4:

And this Irish folk song shifts between 9/8 and 12/8:

In experimental jazz of the 1960s, there is often a complete absence of discernible metric form. As the great jazz pianist Mal Waldron said, “We were talking about freedom, and getting out of jails. Bar lines was like going to jail for us. So everyone wanted to escape from that.”