Frozen Goodies - An advent calendar to get the chance to win daily prizes
Advent Calendar - A fun and interactive calendar
Syndical - Automatically publish events across a range of platforms
24 Ways - An advent calendar for web geeks
Planable.io - Planable is the command center of social media campaigns trusted by agencies, freelancers, and marketing teams, that allows you to easily create, collaborate, get approval and schedule posts for your social media campaigns.
UXmas - An advent calendar for UX folk