Severance is an official a roleplaying schema for Clockwork set in the world of a zombie apocalypse. The schema was originally made during Novalus, and was updated until Garry's Mod 13 released. After GM13, severance was the only schema not to be ported to GM13. Severance's story is a mix between 28 Days Later and Left 4 Dead, but it's plot line borrows mostly from Left 4 Dead.
As of right now Severance is not available for purchase or download from Cloud Sixteen; however, Cloud Sixteen's developers are working on remaking the schema for purchase. The schema is expected to release Summer 2016.