SCADA platform
Two SCADA servers that take over from each other, with failover tested both ways. The spec called for a Windows cluster and a domain the site didn't have; I met the same recovery objective without them and handed over the runbook.
Linux servers, networks and backups for companies of 10 to 100 people: kept in code, monitored, with restores actually tested.

Two SCADA servers that take over from each other, with failover tested both ways. The spec called for a Windows cluster and a domain the site didn't have; I met the same recovery objective without them and handed over the runbook.
All of it runs in my homelab first.