It was open sourced as Apache Wave when Google shut it down.

Years later Apache moved it to read only because of low community activity.

The archived git repo on GitHub remains available to clone and revive as a fork.

This doesn't explain the lack of marketing. Apache isn't exactly known for pushing tech. Google never tried to improve on gmail.

	▲	QuantumNomad_ an hour ago \| parent [-]
		Sorry if it wasn’t clear, I was adding this info for context and for anyone who hopefully feels inspired to pick up Wave and make something from it given that it was all open sourced and all. And I figured that in the chain after your comment about it having been useful looking all along was a natural place to add this additional info and link.