Devuan GNU+Linux is a free operating system started as a fork of Debian. Instead of working on top of original Debian, Devuan implements a fork without systemd, an init manager developed by Red Hat and later adopted by other GNU/Linux distributions. The target of Devuan is to free operating system from all the complexities involved while integrating with systemd.
Just like Debian, Devuan development is also carried out in 3 different branches, namely stable, testing and unstable. Current stable branch is Jessy, testing branch is Ascii and unstable branch is Ceres.