Electronic Engineering Tool is a Web-based tool that includes an electronic formula calculator and converter functions. It very useful when working with electronics, both for engineers and amateurs. For example, it includes converters for dBm-to-Watt and Fahrenheit-to-Celsius, and it can calculate Ohm's law, filters, thermal resistant C/W, SWR, coil inductance, capacitor capacity, and more.
PHP Keno Simulator is a payout ruleset simulator for the classic game Keno. You can tune the payout chart to fulfill your "house advantage" or you can just calculate for fun (predefining the correct payouts) what the odds of winning are and how much your local casino is making for its owners.
PhpMathPublisher is a system for publishing Web pages that include mathematical expressions. Webmasters only have to install some fonts as no CGI scripts or LaTeX programs are required. Each formula is transformed into an image and the generated Web pages can be displayed by all browsers. It can be easily used in a CMS, blogs, and forums.