Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.
NetBox - NetBox is an open source web application designed to help manage and document computer networks. NetBox was developed specifically to address the needs of network and infrastructure engineers.
HaCi - HaCi is an IP address / network administration tool with IPv6 support.
Gestioip - GestióIP is an automated, Web based IP address management (IPAM) software.
Port Authority - A handy systems and security-focused tool, Port Authority is a very fast Android port scanner.
phpIPAM - phpipam is an open-source web IP address management application (IPAM).