The sub-class xUnit.js.Attributes is a specialized version of the xUnit.js engine, which implements and parses the c# style attributes provided by System.Script.Attributes from the System.js library.
xUnit.js.Console includes strategies for the console runners of several common engines, such as SpiderMonkey, Rhino, V8, JScript and Chakra, making automation and continuous integration a simple shell command and increasing confidence in tests of cross-engine code. The xUnit.js.Console runner implements the xUnit.js.Attributes engine, allowing for simple, test-local registration familiar to C# developers. Unlike many other framworks, the xUnit.js console runner does not require a webserver - or even a browser - to run tests. Tests are file I/O based, leading to better boundary isolation, clearer dependency visualization, and faster load and run times.
xUnit.js.Gui implements the xUnit.js engine in a webpage runner, allowing tests to be run in individual browsers. This can facilitate debugging for test writers familiar with the developer tools of a given host. It also allows for browser-specific confidence tests, and coverage for common discrepancies with legacy or non-standard browsers, such as the eventModel.
For additional customization, the engine can be implemented directly, for, e.g., integration in an existing test registration system.
You're probably looking for the console quick-start guide.