Via Frank Meeuwsen I came across a.gup.pe which says it creates instant groups for Fediverse.

• You can join groups by following a group account like @grouptopic
• Mentioning a group’s name will get it distributed to all followers of that group
• Any mention of @sometopic that isn’t a group yet, will automatically create that group (much like my 33mail set-up does for email addresses.)

It seems to me it basically works as a repeater. Mentioning a group’s name will get your message boosted to all those who follow the group’s profile. Basically it boosts all posts on a topic you follow into your home timeline. Different than #tags because to follow those I need to set-up an additional column in my Mastodon interface.

When groups are small then this is potentially useful. But big topics will attract spammy behaviour soon I suspect. Suddenly you have the type of asymmetric amplification that otherwise doesn’t exist on Mastodon. Moderation is not done on the side of gup.pe I think. Anyone can send to the group, not just followers so there’s no route to moderation even. You’d need to mute or block unwanted boosts yourself. The flipside is that it may speed up discovery of new interesting accounts, and allows the type of group interaction that would otherwise require being e.g. in the same instance to be able to find/cluster together. I fear that noise easily will overcome such groups, but for now worth an experiment. I’ve created and joined a few groups from both my personal and work accounts, to see how it plays out over time.