Redmine

I think its a usefull feature to filter activities by user, +1 for this

The filter is already implemented. Go the user's profile and then you can click 'activity' to navigate in the user's activity.
http://www.redmine.org/activity?from=2011-01-14&user_id=1

Aha, so it is. Thanks Jean-Phillippe.

Then my request would be to have this existing functionality in one place, and at a more visible level.
i.e. add the filter ability to the project's main activity page.

In the mean time I will use this.

From my experience, it would be useful to have a similar filter available for activity as for issues, i.e. selecting a set of users to see (or not see) and a date range at the very least, but possibly tracker, status, priority and possibly other fields.

+1 for the ability to filter the activity view by multiple users at once; that is currently not possible with the &user_id parameter. We would use that for quality control monitor the contributions of our less experienced developers.

+1 to have issue filter synced with activity

+1

+1 by Tracker