ELI5 why/how this happened:
https://www.reddit.com/r/cyanogenmod/comments/5k9qr7/somebody_eli5_why_cm_is_shutting_down/?sort=confidence

CM archives & mirrors:
https://www.reddit.com/r/cyanogenmod/comments/5kfo0m/the_cyanogenmod_archives_full_downloads/?sort=confidence

Forked as LineageOS – https://github.com/lineageos
https://www.reddit.com/r/cyanogenmod/comments/5k4dns/a_fork_in_the_road_cyanogenmod/?sort=confidence