Open source projects on vcalendar; vcalendar products?

Hi,

Excuse me if this has been discussed recently. I have two questions on
vcalendaring:

1. does anyone know about open source projects which concentrate on
vcalendar?
2. on the IMC website there is information on iCalendar and vCalendar,
including references to RFC's. What I could not find is an overview of
products/vendors and the standards they support (e.g. iCalendar, iTIP,
iMIP). Does it mean such an overview does not exist?

Regards,

Rolf E. Sonneveld
Sonnection B.V.