Mocha falls down when you have to create your tests dynamically, because Tests in Kava are Tasks, and Suites are TaskGroups, Kava will always know which tests are for which suite. Works tremendously well, with a modular architecture. Also works in the browser.
Execute event listeners as TaskGroups, adding support for asynchronous listeners, parallel execution, and completion callbacks. Event Emitter Grouped is great for plugin infrastructures.
A static site generator that uses TaskGroup and Event Emitter Grouped heavily to accomplish isolated asynchronicity — such that when a plugin fails, it doesn't bring down everything.