Open source differencing and merging tool for Windows
Open source frontend for MySQL, MariaDB, PostgreSQL and Microsoft SQL Server
Data center information management
Open source and web-based IP address management (IPAM) and data center infrastructure management (DCIM) tool.
Open source email and news client for Windows and UNIX like systems
Integrated Development Environment
Software development platform written in Java which supports Java, PHP, C/C++ and HTML5
Open source packet analyzer for network troubleshooting
Open source email and file encryption for Windows using GnuPG public-key cryptography
Open source password management tool
Spy Ad and invisible tracker blocker by EFF
Open source, tabbed, multi-protocol, remote connections manager
Windows Secure Copy, open source SFTP, FTP, SCP client for Windows
SSH and Telnet client for Windows
WiFi network scanner
Not open source but free to use WiFi network scanner/monitor
Measure bandwidth and performance of a network
Port and security scanner including host discovery and OS detection
Web application security reconnaissance tool
Debian is a free and open source operating system.
FreeBSD is a free and open source operating system based on Berkeley Software Distribution.
OpenBSD is a free and open source operating system based on Berkeley Software Distribution.
OpenIndiana is a free and open source operating system derived from OpenSolaris.