Microsoft.
Had to move away from Microsoft products for a while after a move to an international client, and you cannot believe how complicated even the simplest things are to do in the absence of Office, Outlook and Teams.
Eventually we decided to migrate over to Microsoft systems and are slowly busy with the processes now. They asked that I become certified in several areas in preparation for the move, and I cannot believe how much that I didn't know about the services and what they were capable of. Where we were running third party sites, apps and documenting platforms, I found that Microsoft basically covers everything - I just hadn't known about it.
It makes the GDPR so much easier than it needs to be.