After about two years in the wild, Google Wave has been declared dead. Several important pieces of Google Wave were open source, and even more of the closed source pieces, will live on elsewhere on the internet and in Google's other services. Despite this, Google Wave, which I consider to be one of the most important and fundamental advances in communication will cease to exist. Google is no longer maintaining and developing Google Wave.
Google seems to have made a lot of mistakes with Google Wave that lead to it's demise. The first mistake was their slow private beta release. With a communication tool designed to replace email and IM and other forms of communication, the tool was almost pointless when you couldn't communicate with those you wanted to. Another mistake was not building a transport mechanism to connect Google Wave to other existing communication tools. Their final mistake that was quite likely the death blow was that their implementation was slow and buggy. Often users of the wave would experience a crash (similar in spirit to "oh snap" from the Chromium browser, but far more frequent.
I'm hoping other tools such as pygowave that implement the wave functionality more fully, with built in federation continue to grow and mature, and I still believe that a threaded dynamic open-ended communication will be the future, and will replace many of the existing tools we use today. We will just have to wait until the market is ready for such an advanced and capable tool.