Your device will instantly notice this and ping your contact's actual device to double-check

• So that means anyone can, presumably silently, check if I'm on a phone call?
• Or perhaps anyone can check if I'm on a phone call with a specific number?
• Or perhaps anyone can check if I'm on a phone call and retrieve the number?

Other than the "silently" part, I suppose the first isn't a lot different than the old style busy signal, but I wonder what Google has in place to avoid abuse of that feature.

Absolutely agreed, though there are some tweaks that could help. Rather than adding identity verification, simply making the existence of parental controls more prominent would go a long way towards alleviating concerns. The guardrails are there, people just need to know to use them.

The niche it fills is that it is a *lightweight* editor which works for rtf files and LF-only text files, which is available without installing anything extra. Starting up MS Word or LibreOffice Writer takes several times longer than firing up Wordpad, which makes the latter far more usable, especially for taking some quick notes or cutting and pasting some snippets.

Gmail allows it, but certainly doesn't make it easy to use. Though you can receive emails with a plus sign, if you want to respond from one you need to manually add it as an "alias". They really should make that automatic, and also let you edit the from address on-the-fly while composing an email.
I wonder if O365 will get this right?

DANE: https://en.wikipedia.org/wiki/... It does exactly that, and using it's Service Certificate Constraints feature would make revocation irrelevant, since you can specify exactly which certificate is valid.

This eliminates a pretty key feature in many contexts, namely that you need that specific device in order to authenticate. Otherwise, it seems hardly any better than just writing down an extra password in any normal text file on your phone.