Copperhead OS is a fork of Cyanogenmod which goal states “to reduce the dependency on Google services and reduce the attack surface by removing software and hardening the low-level system.” As a result they stripped out a lot of Cyanogen rom features which “phone home” or talk to Google servers. Currently Copperhead OS is only available for the Google Nexus 9 tablet, Nexus 5x, Nexus 6p and the Google Pixel. Copperhead sells the Nexus 5x and Nexus 6p with Copperhead presintalled. Or you can download it now if you have one of the listed devices and follow their instructions to install Copperhead.
Copperhead OS attempts to mitigate vulnerabilities and make exploits unreliable by integrating the PaX kernel and open OpenBSD. Also each individual service and app is given a unique randomized memory process rather than using a global template layout and canary values reused for all applications until a reboot. They also state that the system code is augmented with memory protection, data sanitization, overflow checks and randomization.
Further, Copperhead OS replaces the system allocator with a port of OpenBSD’s malloc implementation. The networking interfaces are given a random MAC address whenever they are brought up. This can be disabled via a toggle in the network settings. Wireless MAC addresses are also unconditionally randomized during scanning (pre-associated). The hostname is randomized at boot by default, and it can also be disabled in order to use the persistent hostname based on the
ANDROID_ID instead. Copperhead’s technical overview can be found here.
Copperhead by default has installed F-Droid as the app store. The operating system does support other third-party app repositories so it is possible for users to sideload others such as the Amazon app store or SlideMe. Flashing the Google Play Store would break secure boot on the Copperhead OS, defeating this security feature. If you can live without the GooglePlay store, most of those games you play and unfortunately the Signal app, this could be the phone for you. You should start by looking at what apps are available on F-Droid and Amazon just to make sure you can live without them if not available. Copperhead accepts donations to help further development and keeping their OS free.