Thanks for engaging with the discussion. With respect to the thought that came to you back in the early email days, I don't mean to be pedantic when I say this, and it may have had definite merit — like ensuring services that are naturally monopolistic due to network effects, are provided by an entity collectively controlled by the public — but an email service wouldn't fit the economic definition of a public good.

An open source codebase allowing anyone to set up their own mail server would be the public good in that domain.

A table that gives examples of private vs public goods:

https://en.wikipedia.org/wiki/Goods#Goods_classified_by_excl...

Public goods:

https://en.wikipedia.org/wiki/Public_good_(economics)

For more complex goods, involving management of platforms, I think the only type of public good that could compete with proprietary offerings is the software that allows people to form a decentralized consensus and run applications on top of it, e.g. blockchain node software and smart contract code, respectively.