That is what they write about themselves:
Today as citizens of the world, we face a daunting array of social and environmental problems ranging from health care and civil rights to global warming and economic inequality. For each of these issues, whether local or global in scope, there are millions of people who care passionately about working toward a solution but have no way of connecting with each other to advance a common goal.
Change.org aims to transform social activism by serving as the central platform that connects likeminded people, whatever their interests, and enables them to exchange information, share ideas, and collectively act to address the issues they care about.
To augment the power of the grassroots networks that develop through Change.org, we help connect these networks to the many nonprofit organizations that are already working to advance worthy causes around the world - over 1 million in total. We facilitate dialogue and collaboration by creating a social network around each nonprofit, thereby allowing people to participate in ways never before possible - by posting ideas and suggestions, engaging in direct dialogue, and organizing communities of donors, volunteer events, and rallies.