OpenVMS
Today, OpenVMS is used in many projects where availability and uptime are critical: These include banks and insurance companies.  Systems staying active for over a decade have been reported. A feature called "rolling upgrade" allows to upgrade software or hardware without the need to shut the system down. A data center that is destroyed will not lead to downtime either, if the system is configured properly. Customers using OpenVMS include banks and financial services, hospitals and healthcare, network information services, and large-scale industrial manufacturers of various products.