Network & IP information

The Official Nmap Project Guide to Network Discovery and Security Scanning. Most thorough guide. 

Analyzes how WiFi signals change as they bounce around a room. From those small signal shifts, it can estimate body position, breathing, heart rate, and movement in real time. 

A tool to get information on IP addresses and ASN details.

An API for accessing comprehensive domain and IP data.

A search engine that indexes internet-connected devices and services.

A search engine for finding and analyzing devices that are accessible from the Internet.