This is Google Wave as a Platform, one of the “Three Ps” of the Wave. The API gives developers a way to plug in to the Wave product and offer new and interesting ways of using waves. For instance at the preview, a software robot developed using the API could be added to a conversation to translate your waves in real-time into other languages.
I’ll be covering more of the ways the API can be used in later posts, but for now I’ll say it’s powerful way to make an already compelling product even more useful.
Google wants developers creating value to add to their product on day one. Hopefully someone enterprising will use the API to bridge the gap between email and waves unless Google does it first.