What is the best collaborative software?

There’s Cube, Central Desktop, etc…

I work for a small organization that needs collab software mainly for shared projects (MS word docs, spreadsheets, etc.), shared calendar, task management and contact lists. I’ve tried a couple and none are very intuitive…. and more for large corporations.

I don’t want too much emphasis on chatting, social media, etc. We’ve got that covered and use those outlets mainly for external communications. We need something for internal things.

I can’t pay more than $5 a month (like I said, very small organization and we’re nonprofit) and would preferably be allowed several users for a workspace…..

If anyone can suggest something good, I would be very grateful! Thank you.