OpenBSD has a pretty long history of eg. limiting attacks through compile time mitigations while making them more usable for every day use compared to specialized "high security" Linux distributions. This can also be seen in patches of third party software (in the ports (packages) system) that often have patches so the code can live with these limitations.
One example of such a mitigation is W^X. Implemented in OpenBSD in 2003, copied later by Windows, Linux and the other BSDs (incl. macOS).
https://en.wikipedia.org/wiki/W%5EX
More recently of course pledge and unveil were also added.
Also in 2003 OpenBSD was also the first mainstream (no research or test OS) that implemented strong ASLR that in 2005 was supported in Linux through third party patch sets.
For a list, see here:
https://www.openbsd.org/innovations.html
Many things were later picked up by Linux distributions, kernel patchsets, compilers, etc.