Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Zimbra - Zimbra is trusted by over 500 million users to increase productivity with a complete set of collaboration tools while maintaining total control over security and privacy.
Event Hunt - Startups and Tech Events Curated By Locals
Microsoft Exchange Server - Microsoft Exchange Server is a messaging and collaborative software product developed by Microsoft.
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Blue-Mind - Blue Mind is a complete solution of company messaging, calendars and collaborative work.