UXmas - An advent calendar for UX folk
CoSchedule - CoSchedule is the #1 marketing calendar that helps you stay organized and get sh*t done. Plan, produce, publish and promote your content.
25DaysOf - A customizable advent calendar, for everyone
Embedly - Embedly helps publishers and consumers manage embed codes from websites and APIs.
24 Ways - An advent calendar for web geeks
Rocketium - A DIY video creation platform. Make videos in minutes using preset themes and templates.