* Fabulous user experience design
* Well thought out page organisation
* Live collaboration is awesome
* Impressive WYSIWYG markdown editor
CSS of pages needs a bit of tweaking (things feel a bit bunched up)
Nuclino definitely deserves to be as popular as Slack and Trello. Like Slack and Trello, Nuclino focuses on one task and does a brilliant job at it. I really hope this stays actively maintained!