Passive TCP/IP Geo-Location - http://geoloc.foremski.pl/
DNS Enumeration - https://github.com/darkoperator/dnsrecon
"Why do we use the Linux kernel's TCP stack? - https://news.ycombinator.com/item?id=12021195
The History of the URL: Domain, Protocol, and Port - https://eager.io/blog/the-history-of-the-url-domain-and-protocol/
Levels of Abstraction: Net, Web, Graph - https://www.w3.org/DesignIssues/Abstractions.html
I'd love to see what cool things you all have found. Anything interactive is a big plus! (Also, there was this one site that talked about designing very efficient netcode for syncing two computers in this 3D visualizer with flying red cubes. I have unfortunately been unable to find it.)