Recommended free collaboration & project management software
I'm looking for a software tool that would help me manage my graphic team. I'm expecting several thing: 

1) Task assignment to particular members of the team
2) File attachement with notifications on change (for those interested in that task)
3) Progress measurement within a task

4) It would be preferable if I could assess the overall progress of one period (milestone) and report to my superiors. 

5) If there was an integrated option to create documentation it would be cool. 

Now we're using:
- Google Wave for documentation (the coolest thing ever!), it's cooperative, easy to use and enables varied file attachments.
- Google spreadsheets to control time flow and task responsibility and additional comments. But when the whole project evolves we cannot rely on one single spreadsheet.

But we suffer from a lack of .PSD repository to host files from the designers. And we can't track changes otherwise than file names with dates included.

Does such an integrated thing exist at all? 

I tried Mantis Bug Tracker, it's cool because it notifies me of any changes, but it seems too complicated for a team of 4 people.

What are your ideas and experiences?
Recommended free collaboration & project management software
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I'm looking for a software tool that would help me manage my graphic team. I'm expecting several thing: 

1) Task assignment to particular members of the team
2) File attachement with notifications on change (for those interested in that task)
3) Progress measurement within a task

4) It would be preferable if I could assess the overall progress of one period (milestone) and report to my superiors. 

5) If there was an integrated option to create documentation it would be cool. 

Now we're using:
- Google Wave for documentation (the coolest thing ever!), it's cooperative, easy to use and enables varied file attachments.
- Google spreadsheets to control time flow and task responsibility and additional comments. But when the whole project evolves we cannot rely on one single spreadsheet.

But we suffer from a lack of .PSD repository to host files from the designers. And we can't track changes otherwise than file names with dates included.

Does such an integrated thing exist at all? 

I tried Mantis Bug Tracker, it's cool because it notifies me of any changes, but it seems too complicated for a team of 4 people.

What are your ideas and experiences?