I don't know a lot about Capsicum, but from what I remember (and see from their website) it adds capabilities to FreeBSD but doesn't make them mandatory. As suc

I don't know a lot about Capsicum, but from what I remember (and see from their website) it adds capabilities to FreeBSD but doesn't make them mandatory. As such, it is a tool to build compartimentalized applications. It does not provide a comprehensive solution to sandbox existing applications, and does not remove the ambiant-authority model. It is a better, safer chroot(). Fuchsia, on the other hand, is built on top of capabilities from the ground up, ensuring that you don't even have a concept of "file descriptor" or "centralized filesystem" to begin with.