Digital whiteboards (eg. Miro, Mural)
Diagrams.net: https://www.diagrams.net/
#CryptPad: https://cryptpad.fr/whiteboard

Prototyping (eg. Figma)
Penpot: https://penpot.app/

Validation (eg. #Google Forms)
CryptPad: https://cryptpad.fr/form
Nextcloud Forms: https://apps.nextcloud.com/apps/forms

File #sharing (eg. Dropbox)
#Nextcloud: https://nextcloud.com/

Virtual communication (eg. Zoom, #Slack, Messenger)
Jitsi Meet: https://meet.jit.si
Element: https://element.io/

Docs (eg. Google Docs, Office)
CryptPad: https://cryptpad.fr/

Tasks (eg. #Trello)
CryptPad: https://cryptpad.fr/kanban
NextCloud Deck: https://apps.nextcloud.com/apps/deck