The Office 365 Power Platform - Automate, Power Apps and PowerBI are central to much of the work we've been using for the last few years
SharePoint - we've been doing SharePoint in its various guises for 13 years.
Teams - It started as chat, but now it's our home from home for team working. Current events have certainly made this essential.
Planner - Just like Teams started small so it is with planner - it just there where you need it, its not a behemoth like MS Project, its not expensive like Jira and its far better to have something everyone can access in a collaborative way, that trying to hang togther spreadsheets.
PowerShell - Not everyone knows but in Microsoft land its unsurpassed in its usefulness.
Delve - I know right, but the org chart has proved to be amazingly useful.
And the whole of Azure, too many different things to mention here.
Security - because the internet!
The tools that help us do our delivery
Jira - A great way to keep everyone on the same page (yes we do know about the To-Do app, but sometimes you need the best tool for a job)
Confluence - Its where we like to put our documents - NOT SharePoint, I know right, well that might change in due course. Still, for now, it is the answer for enterprise-grade documentation.
Github - It's part of Microsoft now, and quite honestly there just isn't anything else that does what it does.
Markdown and Graphviz - maybe you'll love them as much as we do someday.
Reveal.JS - because we don't like PowerPoint
Zoom - I know I know, what about security and shouldn't we be using Teams for this - well yes, but Teams doesn't yet have fl* exible break out rooms, and oh my that makes a big difference.
Gridsome - we made this site with it, and we have a thing about Vue, so it was natural that we used the Vue version of Gatsby.