Extend calendar functionality in Horde groupware

We'd like to extend functionality of Kronolith - a Horde groupware calendar application to fully support event and response states offered by Microsoft Outlook. The final application should support the following: - Setting 'Free/Tentative/Busy/Out of office' event states via the web gui and via the synchronization URL using Funambol plugin - Displaying 'No info/Free/Tentative/Busy/Out of office' attendee states - Respond to event invitations with 'Accept/Tentative/Decline/Tentative and propose new time/Decline and propose new time' states via the web gui - Accept responses of above types via the web gui - Send and accept invitations in MS Exchange-compatible format