The apps
The Mac and iPhone apps connect to your own Docket server. Set that up first.
Docket is invite-only during the beta. The downloads are on your personal invite page, so there is nothing to download here.
Docket for Mac
A native Mac app, signed and notarized by Apple, that talks to your server: your overview of what needs you, fast search across every account, the reader and compose, and approvals for what your agents want to send. It keeps itself up to date.
Docket for iPhone
The same on your iPhone, with notifications for the mail that matters. It is on TestFlight during the beta; once you have an invite, ask for a TestFlight invite.