WordPress Agenda based on user profiles

I am trying to build community blogs with WordPress. One of the features that would be very nice is a WordPress Agenda plugin that would enable my users to update events and place them on a shared agenda, without leaving the WordPress weblog.

It’s a simple idea

A registered user or a user with a certain level or role, should have a tab in the admin section which says Agenda. At that location he can upload an event on a specific date, select the events category and add some text and links maybe an image (e.g. automatically resized to avatar size 80 px x 80 px). In the end he post it onto the front-page where it shows up in the weblog agenda.

Visitors of the website can browse though the agenda by date and category. Registered users see a link where they can add a agenda event themselves. There should be a distinction between old agenda events and events on future dates.

Very nice adds would be if visitors can e-mail an event to a friend, registered can notify other users that they will attend this event (like you can do at upcoming), visitors and users can comment on an event, everybody can social bookmark the event (e.g. on digg, delicious). An other nice feature would be a sidebar widget which shows today’s and upcoming events placed on the weblog’s agenda page.

My question

I’ve found a plugin that does some of the above, it’s Robert Gaal’s WoogleCal plugin. But the plugin is using Google. It’s a nice and simple plugin but it does not allow registered users to share an event calendar / agenda on the weblog without leaving the site. Therefore it complicates the use of the agenda and in the end many users find it to much of a hassle to use. In short it is not suitable or intended for community use

Does anyone know if a plugin like the above already exist for WordPress?

If somebody is willing to build a plugin please contact me, I will certainly test it and donate a humble amount of my bursary. Unfortunately my php skills are not good enough to build a stable plugin myself.