Lineage OS, comprised of former CyanogenMod maintainers and developers, have started pushing out custom ROM builds for a few Android devices. This includes the Google Nexus 5X, Nexus 6P, Moto G4, Moto G4 Plus, Moto E, Nextbit Robin, OnePlus One, Xiaomi Redmi 1S, Xiaomi Mi 3W, and the Xiaomi Mi 4. There will be more devices with custom ROMs coming, but this is the group that Lineage OS is starting off with.
Since Lineage OS is basically a reincarnation of CyanogenMod, the numbering is the same as CyanogenMod. For instance, there is Lineage OS 14.1 which is for Android 7.1 Nougat, where as Lineage OS 13 would be Android 6.0 Marshmallow and so forth. There are also a few builds that are labeled as "Experimental" and these are supposedly .zips that can be flashed over an existing installation of CyanogenMod 13 or 14.1. This is good for those that want to get Lineage OS, but don't want to wipe their device and start all over again. There will be release candidates for Lineage OS just about every week, at least that's what the team is promising right now, that may change over time. Additionally, when you install a Lineage OS ROM, you won't have root right away. The team will release a flashable zip to make it easy to root your device though. And since the device is already rooted to install Lineage OS, there won't be any issues with Lineage OS being available for devices that can't be rooted.
For those that followed along with CyanogenMod, Lineage OS is going to feel very familiar. You'll have the majority of the same features included in Lineage OS builds, and they will be somewhat stock Android, at least in appearance and functionality. There are plenty of added in features - some of which may not make the trip to Lineage OS, while others will. You can download the latest builds for the devices mentioned above, using the link below. Remember that by flashing a custom ROM, you are essentially voiding your warranty, since you do need to root your device to do so and that itself voids your warranty.