Shared Spaces is a Google Labs product, and instead of centering around the conversation like Google Wave, Shared Spaces is more centered around a particular gadget. You can create a space around a map to collaboratively plan a trip, or around a mind map gadget to brainstorm about an idea.
The slideshow below shows a little about Google’s idea of a shared space:
It looks like Shared Space uses Google Buzz in the background. I’m also not sure if it’s possible to make Shared Spaces invite-only, or that anyone who guesses the URL can participate. I’ll let you know more once I’ve played a little more with it.