Antifragile means that whenever something bad happens to the system (i.e. an airplane crash), the system gets stronger by design. A robust system is just a system that is resistant to bad stuff happening (but does not necessarily improve once it happens, or at least it's not built that way).

I'd argue that most Western government institutions (say, governments that have been around for 200+ years) are what you'd call "robust"; likely churches (the Catholic Church, since it's quite centralized), as well.