Search, Maps, Gmail, YouTube
Chrome is arguably a monopoly if you segment desktop web traffic, but iOS Safari is such a large percentage that Safari can't be ignored.
People will disagree with email - but I challenge you to go look at email threads you're on and see what % of the emails are @gmail.com - not to mention G Suite addresses you don't know are Gmail. Outside of enterprise, there's no alternative.
Not bad either that Android and Chrome are duopolies at this point.
A bunch of people have listed Gmail on their lists, but Gmail is not even close to a monopoly, even in consumer email. https://email-verify.my-addr.com/list-of-most-popular-email-...
- that's from 2016
- that seems to be worldwide (I see for example swiss and french providers in the list), which isn't necessarily relevant. Gmail can be a monopoly in the US for example, while not being one worldwide.
Unfortunately I cannot find better numbers, if someone does that would be interesting to discuss.
While I'm sure we could disagree on if Google actually has a monopoly in these domains, I think it's obvious they have a _substantial_ foothold.
Though technically they also have YouTube and do monetize it.