Replicant has previously released an SDK for 2.2, 4.0 and 4.2 in the past, but now says they will not release an SDK for version 6.0 because there is something better. Instead, they'll be using the Android SDK that ships with Debian.
Replicant was first updated to 6.0 Marshmallow back in August of last year, and today they have released some development updates. They've added support for the Galaxy S2, and made some improvements to the graphics rendering, toolchain, and security/privacy enhancements.
Replicant is free and open source operating system based on the Android mobile platform (so it strips out all of the proprietary code).
The operating system has been stuck at Android 4.2 KitKat for a while, but now we're hearing news that it's being updated to 6.0 Marshmallow thanks to Wolfgang...