JS Measurer measures a webpage's width and height interactively. It lets the user define an area in the page by dragging the mouse pointer. The object renders the area outline as the mouse moves, showing the width and height of the area in pixels, as well the coordinates of the top-left corner of the area. A bookmarklet is also available, so this object can be used as a link placed, for instance, in the browser toolbar.
JABM is a Java API for developing agent-based simulation models using a discrete-event simulation framework. It has a simple architecture in which agents are represented using plain-old Java objects (POJOs). Simulations are configured via dependency injection using the industry-standard Spring framework, thus allowing attributes of any object in the simulation to be specified as random variables to be drawn from a specified distribution without having to write any Java code. Attributes of any object can be specified as independent variables or treatments with a given range of values, and experiments with different treatments can be easily parallelized using, for example, SGE.
QMentat helps you practice mental arithmetic. It uses arbitrary-length fixed point arithmetic, and can handle any size numbers, only limited by the size of your screen (and in the case of division with an integer result, the speed at which the number can be factored). It is also quite configurable, allowing you to tailor the questions to your needs.