Kalzium

Kalzium describes itself as "your digital replacement for the periodic table on paper." It displays information from the periodic table in a variety of ways, and it offers a molecular weight calculator, 3D molecule editor, an equation solver for stoichiometric problems and more. (Note that in order to use Kalzium on Windows, you'll need KDE for Windows.)

Step

With this interactive physics simulator, you place some objects on the screen, add some physical forces, and then see how they interact. It covers classical mechanics, particles, springs, gravitational and coulomb forces, collisions, molecular dynamics, and much more. (Note that in order to use Step on Windows, you'll have to download KDE for Windows.)

EJS Modeling

Easy Java Simulations (EJS)

Easy Java Simulations (EJS) is a Java program that can be run under any operating system that supports a Java Virtual Machine (VM). Because Java is designed to be platform independent, the EJS user interface on Microsoft Windows, Macintosh OS X, Unix, and Linux is almost identical.

Pylot - Open Source Software testing tool

Pylot is a open source performance and scalability testing tool which runs HTTP load tests and generates concurrent load (HTTP Requests), verifies server responses, and produces reports with metrics.