UMLet is a lightweight tool for rapidly drawing UML diagrams, with a sound and pop-up-free user interface. UMLet lets you draw diagram sketches quickly, teach UML with a simple user interface, and export diagrams to SVG, JPG, PDF, and LaTeX-friendly EPS. It features a fast, text-based way of editing UML elements.
MonteCarlito is a free Excel-add-in (Windows and OS X) to do Monte-Carlo-simulations. It features statistical analysis of simulation runs (mean, median, standard error, and skewness), histograms, direct output to an Excel spreadsheet, and a high-speed simulation mode with minimized windows.
SQLet allows you to directly execute SQL on multiple text files, right from the Linux commandline. In one single command, you can read in text files (with or without header lines) and perform arbitrary select statements, including joins over several files. SQLet can thus replace awk or grep in some instances.