Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.

Cobalt Strike - Advanced threat tactics for penetration testers.

Angry IP Scanner - Open-source and cross-platform network scanner designed to be fast and simple to use

Shodan - Shodan is the world's first search engine for Internet-connected devices.

Advanced IP Scanner - Advanced IP Scanner shows all network devices, gives you access to shared folders, and can even remotely switch computers off. Download it Free.

Censys - Censys helps organizations, individuals, and researchers find and monitor every server on the Internet to reduce exposure and improve security.