This is a comment about Groups.io from the fboats site - looks good but looks vulnerable at this stage in its development. Maybe picking up enough Yahoo transfers will make it a larger less vulnerable company.
"Group.IO PROS:
I own/moderate several Yahoo groups and I have been testing
groups.io. I built a small test group recently. I bought a paid subscription to get a small gtroup which is presently waiting in the queue for transfer, in order to test the process. I also have been running a free a forum and I am testing the backup/export capabilities.
Based on my testing, I can confirm that
GROUPS.IO can accomodate files and photos, both inline and as attachments. All can be backed-up in their native file formats. Messages can be archived in mbox format.
So far, I like what's been happening but I am still waiting for the transfer of the one group, so the jury is still out.
Group.IO CONS
Groups.io is a one man show, literally. The support community consists of one company owner and two volunteers. While I have found the support team to be very responsive, and the product robust, the risk of them going offline is great. There is not a stand-alone version of the software. "