This presentation is an overview of many different mitigations spanning ~27 years. Some are quite widely implemented. I'm less familiar with the newer stuff, but here's some I've run into.

No-exec stacks: some UNIX machines, tons of systems today.

w^x: win xp+, Linux, several RTOS, OpenBSD, lots of others

aslr: requires MMU. OpenBSD, contemporary Windows(but partially opt in?), Linux.

X-only: Arm has supported X-only for their embedded stuff for a while, and it's fairly lightweight, though you lose PC-relative loads.