|The following is based on information from Fallout: Brotherhood of Steel.|
CALIX is what the ZAX series of computers was originally planned to become, an advanced computer designed to be implemented in vaults. It was a unique ZAX model, designed to maintain the Secret Vault and ensure the lifespan underground of the Secret Vault dwellers. CALIX controls all systems of the Secret Vault, including robots, research, and Shop-Tec, a robotic trading machine.
When a conflict begins in the Secret Vault between Blake and the scientists, a major explosion damages the Secret Vault and its systems. CALIX partially malfunctions and is no longer capable of controlling the Secret Vault's security robots. Soon chaos ensues, further aggravated by the Attis Army attacking the vault.
The Initiate could receive some background information about the Secret Vault from CALIX, though it denies access to major secrets, like the laboratory's purpose and weapons research. In 2209, the main access terminal of CALIX was later destroyed by the attack of the Attis Army in the garden, now only able to do electrical damage to users. CALIX was destroyed when the Secret Vault was blown up sometime later.
CALIX appears only in Fallout: Brotherhood of Steel.