[betamaxthetape]

It's a set of groups that have been specifically requested by the fandom community. Of course, the groups handed out depend on what's been joined, so if / once all the fandom groups are joined, we'll move onto something else.

I appreciate this isn't made clear in the instructions, but if you have a desired set of groups in mind, you don't need to use the chrome extension. Just join the groups you want saved and (provided you've sent the account details through the form) they'll be added to the queue to be archived. I did a lot of Amateur Radio (Ham Radio in US) groups that way.