Coconut AIO is part of the Coconut project at Codehaus. The focus of the coconut project is highly concurrent internet services. This includes things like caching, multi-threaded IO, etc. Sadly, the AIO component of Coconut is no longer developed, and is considered discontinued. Even the Coconut website no longer references the Coconut AIO package.
One of the things I liked about Coconut AIO was that it was based around java.util.concurrent.Future objects. This provided more accessibility to junior developers since the whole model behind selector threads, content filters, and registering socket interests can be rather daunting.
Maybe the Coconut group will revisit the AIO package after they finish work on their caching services.