Their cloud offering is fairly poorly promoted and no one seems to notice it exists. You have mail, contacts, calendar, photos, drive, notes, reminders, documents, spreadsheets, presentations and device location all via their web interface all of which real time sync with desktop and iOS apps.
But note as always that the apps are Apple design centric which means they have intentionally limited feature sets and not many bells and whistles compared to some competition. If you learn to meet them in the middle they are monumentally powerful however, particularly in combination with Shortcuts app. I have a lot of event driven and schedule stuff set up with that which keeps me organised and kills a lot of routine tasks for me. I could not have set this up with Microsoft or Google ecosystems without resorting to actually writing horrible API manipulating code and having to host it somewhere. I just tap some shit out in the shortcuts app on my iPad or iPhone or Mac and it just works quietly and reliably. It's not perfect of course due to pre-existing expectations as a programmer mostly, but it's a real hidden chunk of gold once you wrap your head round it.