One better, I used to work at a place that had two NTP appliances. They sat on the network and had GPS antennas and all that, but they were some kind of hardened certified appliance things.

About the SyncServer S600 Microsemi’s SyncServer S600 is the industry’s only network time server with security-hardened NTP Reflector technology, supporting extremely high capacity and ultra-accurate ...

Arrow Electronics announces an exclusive distribution agreement with NEC Europe and NTP Software for the E-Tiering Cloud Appliance.