#activitypub platforms serves as pretty powerful groupware as well.
If you have say a #VPN accessible #LAN inside a #VPS or the #cloud and you've got control over name resolution and certificate authorities, you can use #Mastodon, #Matrix, #PeerTube, etc as an internal organizational tool.
It might be seen as overkill, but if you want to use ActivityPub as an internal messaging and communication method, you can pretty much set up whatever platform suits your need.