OpenBSDs pledge is so simple and nice to use. I really wish Linux would incorporate it. Seccomp is a nightmare to implement.
The simplicity of pledge is good enough for 99% of use-cases I'd wager AND easy to add to existing code.
https://github.com/jart/pledge
https://justine.lol/pledge/Definitely a nice project, but I don't know if I'd use it in production.