CiviCRM
While many other systems are focused on the needs of businesses, CiviCRM is an open source CRM developed specifically for non-profit organizations. As of now, more than 10,800 organizations from all over the world have used it to account for 116 million donations. CiviCRM includes features that make it a lot easier for non-profit organizations to centralize their constituent communications, as well as build a bigger donor base and manage it efficiently. The CRM offers a variety of website integration features that will be useful for organizations primarily using the Internet to communicate with their donors. It has full customization and expansion features and is maintained by thousands of people from all over the world. Organizations that deploy it retain complete control over their data, as they can install it on their own hardware or a third-party hosting provider's servers, making it easier to guarantee a high level of security.