iNet - Network Scanner - Explore your network !
Fing - Discover which devices are connected to any Wi-Fi network, map devices, detect intruders, assess...
Technitium MAC Address Changer - Technitium MAC Address Changer (TMAC) is a freeware utility to instantly change or spoof MAC Address of any network card (NIC).
Angry IP Scanner - Open-source and cross-platform network scanner designed to be fast and simple to use
I2P - The I2P network provides strong privacy protections for communication over the Internet.
Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.