360o feedback system

What I would like from a 360^o feedback system:

• All people in the organisation are set up as users on a intranet hosted feedback system
• Each user can nominate other users (e.g. those they have work with, worked for, or had working for them) to give them feedback
• Users can also nominate themselves to give feedback for other users
• Users can nominate other users to give feedback to their direct reports
• Certain relationships do not require nomination (e.g. line manager) - for these relationships feedback is mandatory
• For nominations, feedback is optional
• Feedback from all nominated/compulsory users is aggregated at the end of the appraisal period, and used for the manager to assess the performance of their direct reports
• Feedback on a particular user is by default hidden from that user (both the content, and that actual feedback has been submitted), but can be seen by both the submitting user and the receiving user's line manager
• Submitting users can opt to have their feedback visible to the recipient
• Users can submit feedback as many times as they like per person in the reporting period
• Users can attach documents when giving feedback
• Feedback may include categories, ratings, etc based on the specific performance assessment criteria of the organisation (thus the design of the system would need some flexibility)