Speccy - Speccy - find the details of your computer's specs. Great for spotting issues or finding compatible upgrades. Download the latest version free.
Fing - Discover which devices are connected to any Wi-Fi network, map devices, detect intruders, assess...
CPU-Z - CPU-Z is a freeware that gathers information on some of the main devices of your system : Processor name and number, codename, process, package, cache levels.
Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.
AIDA64 - AIDA64 is a system information, diagnostics and benchmarking solution for Windows PC.
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.