Adubya

I like the Nextcloud suggestion.

Still if you’re open to hosting or can find hosting service, then Odoo Community could work. It’s a ERP/CRM suite with several useful modules, including:

• Discuss (Slack-like messaging with file attachments)
• Calendar, To-Do, and Project for task management
• Website & eLearning modules for additional functionality

Its unfortunate that some modules & features are withheld for selling people on Enterprise. Could be soltuion to look into but is proably overkill. Similar to Odoo, ERPNext doesn’t do feature lockout but I don’t know if they have similar modules or not.