In progress — this area is still being built; some actions described may not be available yet.
The One Messages is the planned desktop app for Messages. It is part of The One Stack. Your MSP will be able to brand it with its own name, so the people using it know who provides it.
Where it stands today
As of today, the desktop app is not available to download. Messages on the web in the Hub is being built first; the desktop app follows. This page will cover install and sign-in when it is available.
See Messages in the Hub for the current state.