Collabora / CODE / Libre Office Online provides the functionality to allow collaborative editing of documents. Spreed gives functionality similar to Skype’s web version. Both have apps that integrate them into Nextcloud / ownCloud. Both are highly desired by many users of both Nextcloud and ownCloud, but both have relatively long and tricky setup/configuration processes for less technical users to set up.
Providing easy install for document editing / audio + video calls are about the most common needs for people everywhere that aren’t provided in YunoHost already.