>Modern Architecture
I wouldn't call FreeBSD (or any UNIX(1971)-like system) modern.
A modern architecture would be something like Genode[0], a multi-server system built around the concept of capabilities.
FreeBSD does have Capsicum [0] though — with file descriptors as capabilities. FDs can be passed between programs over UNIX datagram sockets.
Processes can enter "capability mode" where only open (or rather: active) file descriptors can be used. There used to be an alternative runtime for FreeBSD called CloudABI [1], with which native programs could be started in capability mode, but it was discontinued in favour of WASI [2] (server-side Webassembly) — which adopted CloudABI's libc API.
0: <https://www.cl.cam.ac.uk/research/security/capsicum/>