EspoCRM - EspoCRM is open source CRM (Customer Relationship Management) software that allows you to see, enter and evaluate all your company relationships regardless of the type.
Cvent - Cvent's event management software provides event planners with a complete solution to increase event attendance and decrease event costs.
CiviCRM - A Constituent relationship management for the Civic Sector
Eventzilla - Eventzilla lets you sell tickets online and manage attendees from one integrated application.
Less Annoying CRM - A simple customer relationship manager made just for small businesses. Manage contact info, track leads, and never miss a follow-up.
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets