Proxmox - Open Source Virtual Environment

Proxmox VE (Virtual Environment) or PVE for short is a freely distributed Linux-based operating system based on Debian GNU/Linux and engineered to by deployed as an open source virtualization computing environment for running virtual machines and virtual appliances.
It is distributed as a single ISO image that’s easy to use, easy to install and easy to configure. The end product will be a full featured server machine based on KVM (Kernel Virtual Machine) and designed for handling virtualization tasks.

Virtual Box – Open Source Virtualizer

VirtualBox is a general-purpose full virtualizer for x86 hardware. Targeted at server, desktop and embedded use, it is now the only professional-quality virtualization solution that is also Open Source. By default VirtualBox will be compiled with hardening enabled. That means all binaries will be run suid root, which is the default behaviour of upstream packages. However, you are still able to disable this by passing HARDENING=no to the script.

GraphCalc

Open Source Calculator for Windows

GraphCalc is an open source computer program that runs in Microsoft Windows and Linux that provides the functionality of a graphing calculator.

Graphviz - Graph visualization

Graphviz is open source graph visualization software. Graph visualization is a way of representing structural information as diagrams of abstract graphs and networks. It has important applications in networking, bioinformatics, software engineering, database and web design, machine learning, and in visual interfaces for other technical domains.