vtiger CRM is an Open Source CRM software for small and medium businesses. vtiger CRM uses open source technologies such as Apache, MySQL, PHP (and other open source projects) to provide a powerful multi-platform CRM solution (works on Linux and Windows).
vtiger CRM provides the CRM features that other commercial programs sell for thousands of dollars, such as: sales force automation, customer support & service, marketing automation (with support for e-mail campaigns), inventory management (with product customization module), security management, and of course contact management and task scheduling.
Prophet, developed by Avidian Technologies, is a CRM add-on that enhances Outlooks productivity by adding more advanced CRM features. It comes in two major editions: Individual (for single use, has three other sub-editions - Personal/Advanced/Premium) and Server (for team use, has two other sub-editions - Professional Server and Enterprise Server). Prophet is integrated into Outlook, so when adding an appointment, contact or a task that is added into your Outlook database too (no need to synchronize like with other external CRM programs).
Constant Contact is an online contact management service with options to follow-up with your contacts via an email newsletter, promotion, event invitation, or to send them online surveys - an easy way to connect with your possible (or existing) customers and find out what you could do to improve their experience with your company.