Free and open source software

Data comparison

WinMerge - Open source differencing and merging tool for Windows

HeidiSQL - Open source frontend for MySQL, MariaDB, PostgreSQL and Microsoft SQL Server

Netbox - Open source and web-based IP address management (IPAM) and data center infrastructure management (DCIM) tool.

Claws Mail - Open source email and news client for Windows and UNIX like systems

NetBeans IDE - Software development platform written in Java which supports Java, PHP, C/C++ and HTML5

Wireshark - Open source packet analyzer for network troubleshooting

XCP-NG - Turnkey Open Source Hypervisor, based on XenServer

LibreNMS - LibreNMS, a fully featured network monitoring system that provides a wealth of features and device support

Gpg4win - Open source email and file encryption for Windows using GnuPG public-key cryptography

KeePass - Open source password management tool

Privacy Badger - Spy Ad and invisible tracker blocker by EFF

Fawkes - Fawkes: Protecting Personal Privacy against Unauthorized Deep Learning Models

mRemoteNG - Open source, tabbed, multi-protocol, remote connections manager

WinSCP - Windows Secure Copy, open source SFTP, FTP, SCP client for Windows

PuTTY - SSH and Telnet client for Windows

Homedale - Not open source but free to use WiFi network scanner/monitor

iperf - Measure bandwidth and performance of a network

nmap - Port and security scanner including host discovery and OS detection

skipfish - Web application security reconnaissance tool

Debian Gnu/Linux - Debian is a free and open source operating system.

FreeBSD - FreeBSD is a free and open source operating system based on Berkeley Software Distribution.

OpenBSD - OpenBSD is a free and open source operating system based on Berkeley Software Distribution.

OpenIndiana - OpenIndiana is a free and open source operating system derived from OpenSolaris.