Free and open source software

Data comparison

WinMerge
http://winmerge.org/
Open source differencing and merging tool for Windows

Database management

HeidiSQL
https://www.heidisql.com/
Open source frontend for MySQL, MariaDB, PostgreSQL and Microsoft SQL Server

Data center information management

Netbox
https://github.com/digitalocean/netbox
Open source and web-based IP address management (IPAM) and data center infrastructure management (DCIM) tool.

Email client

Claws Mail
http://www.claws-mail.org/
Open source email and news client for Windows and UNIX like systems

Integrated Development Environment

NetBeans IDE
https://netbeans.org/
Software development platform written in Java which supports Java, PHP, C/C++ and HTML5

Packet Analyzer

Wireshark
https://www.wireshark.org/
Open source packet analyzer for network troubleshooting

Privacy

Gpg4win
https://www.gpg4win.org/
Open source email and file encryption for Windows using GnuPG public-key cryptography

KeePass
http://keepass.info/
Open source password management tool

Privacy Badger
https://www.eff.org/privacybadger
Spy Ad and invisible tracker blocker by EFF

SSH/SCP clients

mRemoteNG
https://mremoteng.org/
Open source, tabbed, multi-protocol, remote connections manager

WinSCP
https://winscp.net/
Windows Secure Copy, open source SFTP, FTP, SCP client for Windows

PuTTY
https://www.chiark.greenend.org.uk/~sgtatham/putty/latest.html
SSH and Telnet client for Windows

WiFi network scanner

Homedale
http://www.the-sz.com/products/homedale/
Not open source but free to use WiFi network scanner/monitor

Network tools

iperf
https://iperf.fr/
Measure bandwidth and performance of a network

nmap
https://nmap.org/
Port and security scanner including host discovery and OS detection

skipfish
https://code.google.com/archive/p/skipfish/
Web application security reconnaissance tool

Operating Systems

Debian Gnu/Linux
https://www.debian.org/
Debian is a free and open source operating system.

FreeBSD
https://www.freebsd.org/
FreeBSD is a free and open source operating system based on Berkeley Software Distribution.

OpenBSD
https://www.openbsd.org/
OpenBSD is a free and open source operating system based on Berkeley Software Distribution.

OpenIndiana
https://www.openindiana.org
OpenIndiana is a free and open source operating system derived from OpenSolaris.

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