I'm trying to find a good calendaring solution for a small (~35 users) organization. Shared calendars, free/busy, and resource management would be required features. We're fine on the e-mail front from both a client and server perspective, so ideally it wouldn't try to supplant our current e-mail system.
Does anyone know of an open-source application that fits the bill? We will be working with Windows clients, so a web interface is preferred. (Sunbird/Lightning have some limitations in their free/busy implementation.)