The Fluent.NET library introduces extension methods to make .NET code easier to read and more fluid to write.

Unitils is an open source library aimed at making unit testing easy and maintainable. Unitils builds further on existing libraries like dbunit and integrates with JUnit and TestNG. Unitils provides general asserion utilities, support for database testing, support for testing with mock objects and offers integration with Spring , Hibernate and the Java Persistence API (JPA). It has been designed to offer these services to unit tests in a very configurable and loosely coupled way. As a result, services can be added and extended very easily.

Examples, tests and standard library for Groovy++. Groovy++ is statically typed extension of Groovy programming language.

Metric_fu is a set of rake tasks that make it easy to generate metrics reports. It uses Saikuro, Flog, Flay, Rcov, Reek, Roodi, Churn, Subversion, Git, and Rails built-in stats task to create a series of reports.

JointJS is a JavaScript library for creating diagrams. The diagrams can be fully interactive. Joint library is suitable for both implementing a diagramming tool as well as simply for publishing your diagrams.

ShareCoffee is a lightweight library for creating SharePoint Apps. It’s fully written in CoffeeScript by using Mocha, Chai and SinonJS.

Wu.js is a library for lazy, functional programming in Javascript. Works great in the browser, and also with CommonJS

Bootstrap is Twitter's toolkit for kickstarting CSS for websites, apps, and more. It includes base CSS styles for typography, forms, buttons, tables, grids, navigation, alerts, and more.

Likno Drop-Down Menu Trees is more than a powerful cross-browser, platform-independent html tree control for your web pages. It's an intuitive way of showing structured information and providing your visitors with the means to manipulate this information in a user-friendly manner.

Hades is a utility library to work with Data Access Objects implemented with Spring and JPA. The main goal is to ease the development and operation of a data access layer in applications.