Jos Poortvliet, Nextcloud:
Nextcloud Flow is designed to help you automate tasks. For example, when a file is added to a specific folder, a shared link to the file could be created and send through Nextcloud Talk into a specified chat room. Or, when a new element (like a file, a chat or a Deck board) is added to a certain project, you get a notification.
...Flow can go beyond files, tying together the various capabilities of Nextcloud. Through an easy API, Nextcloud applications like Calendar, Mail, Talk and Deck will be able to provide actions and triggers for users to use. This means that more and more apps will be able to offer integration, so users can configure Nextcloud to respond to a wider range of events with an ever growing amount of actions.
Flow will be a part of Nextcloud 18. We have just started working on this release, but Flow has been under development for while already. A first tech preview is available as part of our development version, downloadable as a daily build. Input from users is very welcome, as there is a wide range of capabilities that could be added and the team is looking for use cases to prioritize. App developers can also get started supporting Flow in their apps!
Derivative, but still appreciated.