Subgraph is in pre-alpha (February 2016) is an OS aims to secure the “endpoints” while remaining easy to use. Based on Linux (Debian Stretch).
Subgraph believes that security and usability are not necessarily
mutually exclusive. One of our objectives is ease of use, particularly
for privacy tools, without compromising effectiveness. Subgraph Mail is
the email client, and it was written from scratch partially because of
usability concerns expressed around privacy tools.
Subgraph OS is based on a foundation designed to be resistant to
attacks against operating systems and the applications they run.
Subgraph OS includes built-in Tor integration, and a default policy that sensitive applications only communicate over the Tor network.
Subgraph Mail is a new desktop email client written from scratch, with its own implementation of OpenPGP built-in.
They are currently looking for alpha testers.