Yes as per as the role based structure is concern its mostly usable when we have a hierarchical users something like
CEO
------ VP
-------------- Sales manager

and so forth so users from any top level can view data from the user under him.

So yes as you suggested concept of team would be nice to have so that groups could be used with co-workers.

So lets dig a bit in that idea.
So users will add co-workers to a team.

Then we have Contacts, Tasks, Projects and Invoices that can be shared with the team.

From the feedback I got the user case are:
- 1) I am the manager I want to see all my team contacts and activity without them having to share them.
- 2) I would like to share invoices with my account
- 3) Sharing contacts feels like an extra steps
- 4) How do I delegate Tasks.

The 3) I get it a lot, in different variations.

How to best answer the user case in terms of simplicity and productivity ?

The 1) seems to me the hardest as like @Abhik you mention it requires a hierarchy.

Will thinks more about all that....

Any suggestions, ideas are welcome

I've thought about this for two days now, and my thoughts are 1. This is a good idea, but 2. We shouldn't make Ofuz too complex.

I wonder if the "co-worker" concept could be replaced by teams or groups? I think having both will be too much.

I can envision a boss creating groups of users, and also deleting members. I can also see people creating their own group of friends for the purpose of sharing.

I vote for the teams/groups model (instead of the "co-worker" concept). It would allow a Director of Managers (if you will) to look at all of the lower level projects and invoices. It would make the items that @philippe mentioned more possible. I can't speak for everyone, in all countries of course, but in the US it is very rare for a CEO (or other "C-Level" executive) to get this granular, they want reports and charts. It is more common though for the VP->Sales Manager or Accounting Manager->Sales Manager hierarchy.

This is definitely my biggest roadblock to adopting the program fully. The idea of creating groups is fine, but someone like a manager or CEO will need to be able to participate in multiple groups so they can have access to the entire organization (devs, sales, support, etc).