If the last mile to a location (no chance to get the latency/bandwidth improved) is the problem or no internet connection to an external CDN is desired only a LAN based local intranet CDN seems to be the way to go.
So what (open source preferable) solutions exist to server some hundred locations with LAN server installed CDN software.
You can use Intranet CDN but it is accessible only inside your company or home, yes you can implement by setting up a DNS and Access it.
Office 1 - example.domain.com -----> 10.10.10.5
Office 2 - example.domain.com -----> 192.168.1.5
Office 3 - example.domain.com -----> 10.100.4.5