There have actually been a surprising number of computing platforms that implement fault-tolerant processing. It's often called "lock-step" execution.

https://www.vmware.com/content/dam/digitalmarketing/vmware/e... (throughout)

https://en.wikipedia.org/wiki/Tandem_Computers

https://www.intel.sg/content/dam/doc/product-brief/high-perf... (page 5)