Google Wave is built around HTML 5, so you'll need to use what Google calls a 'modern browser' — Chrome, Safari or Firefox (or IE with Google's new Chrome Frame plugin). Once you're using Wave, you'll see a list of currently accessible waves, along with your current contacts. It's just like using a cross between IM and a wiki.
Waves are collaborative documents, composed of 'wavelets' and 'blips'. They're all XML, so external applications — which Google calls 'robots' — can join a wave, becoming a part of the conversation. This is the Wolfram Alpha robot at work, answering queries and adding supporting information to the wave.
Wavelets can be edited collaboratively, in real time. You can see just who's edited a section, along with what they've added (and also watch them working from another machine!). Google has included tools for adding maps to a wave, and all participants can manage the control — including editing zoom levels, locations and adding pins.
Gadgets are in-wave applets that can be used collaboratively. The current selection is quite small, but you can also bring in gadgets from other sites — all you need is their URL. It's not the most user-friendly of approaches at the moment, and we'd expect Google to increase the size of the Gadget gallery when Wave gets its public launch.
Google's Tweety the Twitbot is one of the more popular robots on the developer Wave. It's a simple tool that gives users a wave that's made up of the contents of their Twitter feed, and at the same time handles posting from Wave to Twitter. Google has made the source of Tweety publically available, so you can use it as the basis of your own Wave robots.
Robots are joined to a wave using what looks just like an email address (which maps to where they're stored on Google's AppEngine cloud computing platform). There's a directory of publically available robots (and gadgets and embedding tools) on AppEngine.
Waves can be embedded in external applications — turning them into collaborative publication tools. Google has already made its embed API available, and developers have produced tools for adding waves to web applications, as well as managing the content in several waves — so you can use private waves to build content, and public waves to share the completed text with the world.
Developers get access to plenty of documentation on just how to build their own Wave applications (and even their own Wave servers). Because Wave is a web application, debugging isn't that easy and you'll need to resort to a mix of different tools to test your own plug-ins. The built-in XML debugger is particularly useful, helping you understand the content of wavelets that your code has created.
One of Wave's more interesting — and potentially useful — features is its built-in time machine. You can scroll backwards and forwards through the history of a wave, seeing how the content in the wave got to be the way it is — and the changes that were made at each stage. This makes it easier to use Wave as a collaboration tool, giving you an in-wave audit function.