Wordpress launched a new platform based on javascript leveraging libraries like Node and React. Matt Mullenweg spelled out more details in his post Dance to Calypso.
I downloaded it from the Github page Automattic/wp-calypso and am still testing it out. If you want to run calypso on a different port after following the installation on a different port use:
On my fish shell
env PORT=3123 make run
On a standard terminal, the below should work (untested)
PORT=3123 make run
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