For some of my projects such as DNS/DHCP servers, routers, firewalls, NTP Servers, or for some Arduino projects, I embed OpenBSD on small footprint and low power consumption machines.
At home I have two networks, one for my family and me and one for my guests. Once you are on the family network you can access our backup server, our music and video server, our printers, etc. The guest network can only access to the internet.
You can build a highly accurate Stratum-1 NTP Server for less than $100 using an old Wyse WinTerm, a GPS and a few electronic components.