100 in 100 Challenge - Get 100 new paid users in 100 days
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
GrowthHackList - 100+ curated growth hacks for makers + early stage startups
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Marketing Examples - A gallery of real world marketing case studies. Updated every day.
Bigtent - BigTent is a web-based organization and communication portal for groups.