CHERI is a hardware architecture and instruction set to add safety-related capabilities to processors. See https://www.cl.cam.ac.uk/research/security/ctsrd/cheri/ In this context a capability means a way to track and enforce which memory area a pointer can point into. Typically this has to be coupled with a compiler which will initialize the capability for each pointer.

Fil-C seems to be a C variant that adds capabilities and garbage collection. See https://github.com/pizlonator/llvm-project-deluge/blob/delug...