It is. The dropdown menu for nodes when managing them from the ACP has an option to move it to a collab.
Where do I start.
GC provides intelligent and granular partitioning of existing site resources instead of trying to recreate them in some other form. Because of this approach, it allows groups to use all apps at their full strength, in their full form, including all configuration features of that app that get added or changed as it evolves.... inherently.
Clubs on the other hand provides an alternate way for apps to offer up their configuration in "club mode".
For example, create a forum in a "club" and you'll be able to set its name and description.
Create a forum in GC and you set its name, description, icon, password, theme, link, post count pre-requisites, order, nesting level, permissions, and everything in between.
Similarly, it supports all apps that follow the container/content model out of the box because it doesnt attempt to know how to intercede with its configuration.
They really are two totally different approaches that result in two different products.
Other key differences that I can see is that GC also partions the permissions system in its full capacity also. Meaning groups are able to define their own custom roles inside the group with all the same moderator permission granularity of the main site assigned to those roles inside the group, and permissions matrices for the group content set up based on those roles as well.
Then theres the whole rules ECA integration. Group memberships and actions can be tied into automation quite easily if needed.
Clubs will be a great way for sites to roll out some basic group participation facilities. And GC will remain the solution for when you want to empower your groups to collaborate using the full power of the IPS4 community suite.