Yasca consists of two components:
* a framework for conducting source code analyses, and
* an implementation of that framework, leveraging custom plugins, FindBugs, PMD, and Jlint
Yasca is a command-line tool. Just point it at your code base and watch it go to work. The output is an HTML file containing all findings.

YAP is a high-performance Prolog compiler developed at CRACS and LIACC/Universidade do Porto. Its Prolog engine is based in the WAM (Warren Abstract Machine), with several optimizations for better performance.

Yakindu is an open-source-toolkit for the model-driven development of embedded systems. Through the systematic use of models, it aims at an integrated development process as well as an increase in quality and maintainability.

The Yahoo! User Interface (YUI) Library is a set of utilities and controls, written in JavaScript, for building richly interactive web applications using techniques such as DOM scripting, DHTML and AJAX. The YUI Library also includes several core CSS resources. All components in the YUI Library have been released as open source under a BSD license and are free for all uses.

xUnit.net is a free, open source, community-focused unit testing tool for the .NET Framework. Written by the original inventor of NUnit v2, xUnit.net is the latest technology for unit testing C#, F#, VB.NET and other .NET languages. Works with ReSharper, CodeRush, and TestDriven.NET.

XUnit is to XML-oriented Programming as JUnit is to Java programs : XUnit uses Active Tags as a simple framework to write repeatable tests. With XUnit, you can well-try and improve your own Active Tags program as well as external XML processes such as XSLT. But you are also encouraged to use XUnit for testing Java programs that are producing XML documents.

A simple javascript framework for building mobile web applications.

Executable, translatable UML (xtUML) is an extension to UML based upon the Shlaer-Mellor Method of Model-Driven Architecture (MDA), which supports a powerful approach to Model-Driven Development (MDD). xtUML.org provides the system design community with access to xtUML editing, execution and translation capabilities, along with a forum to advance the use of this methodology. Find the BridgePoint tool along with models, training materials and community discussion here.

Open extensible system analysis report tool for Java, based on numerous open source analysis initiatives. The XML/XSL batch-processing framework produces integrated HTML/SVG reports of the systems current state and the development over time.

XPlanner+ is a web-based project planning and tracking tool.