[9.21.16 Not a complete or comprehensive list – more to come]
Google Drive
The convenience Google Drive has brought to me has increased my productivity by leaps and bounds. The suite of productivity tools providing the ability to share documents, collaborate with others, and access it from anywhere is underappreciated.
Evernote
It seems to me there are two schools of thought when it comes to Evernote. Either it's amazing or it's too complicated at first glance and people run away from it. This is an tool and once you understand the basics you will be surprised by how much more it can do outside of taking notes.
Dropbox
Everyone should have a dropbox account. Have a place to store your files remotely and access them through the website or mobile app. You can easily share files and unlike Google Drive, neither party has to have a Google account to participate.