https://en.wikipedia.org/wiki/Tagged_architecture
https://researchers.mq.edu.au/en/publications/symbolics-ivory-processor-a-40-bit-tagged-architecture-lisp-micro
https://www.devever.net/~hl/power9tags
Used this years ago on an IBM AS/400 minicomputer, but all the engineering elegance was hidden to make things look same as they always did (RPG400, COBOL). :-(
CHERI is a modern implementation on ARM, looks most likely to show up on my desk sometime.