CiviCRM is an open source CRM (constituent relationship management) system that expands the functionality of your website in many different ways. It’s built specifically for nonprofits, so you won’t find yourself having to try to shoehorn your organizational workflow into a business-oriented model (as some find themselves doing when using Salesforce or similar CRMs).
Even better, it’s built to be extremely flexible and customizable: you can create custom fields, location types, contact sub-types, relationship types, financial types… and more, all customized to your nonprofit’s specific needs. There are no hard-coded limits on the numbers of contacts you can store – and likewise, no arbitrary limits or thresholds that trigger a higher monthly fee. (We’ve heard horror stories of groups that start out with – for example – a “Nonprofit Success Pack” on Salesforce and then when they outgrow it find themselves trapped in what turns out to be a very expensive system, or wanting to expand functionality with “apps” that end up unexpectedly costing hundreds of dollars a month. Here’s one example that was shared publicly.)