Google Space it's a way for groups to quickly share text, , images, videos or links.
This news was announced yesterday by Google and is available as a web service and in form of native applications for Android and iOS.
If you want to access to Spaces then this is not protected.
The only security that prevents uninvited users from accessing a Space is a random invite string.
The customization options let you to change the header graphic, change colors, and add a name to a space, but that is about it.
Google Spaces is part Google Plus and part Wave and will come with new features.