Custom Reminder for Sharepoint 2010 Calendar Events

Custom workflow needed to generate alert to assigned recipients. The custom reminder should have the following capabilities: 1. Works with Sharepoint native calendars 2. Allows multiple reminders (for example, 90 days, 60 days, 30 days before due date) 3. Alerts conditionally triggered by available calendar event columns (such as category, start time, etc...) 4. Deployed as a feature so that can be activated/used at site collection level. Additional detail available upon request. Thanks