Popular consumer online genealogy resource that includes birth, death, and marriage records as well as searchable manuscript census records for the U.S. 1790-1930. Similar records are also available for the U.K., Germany, and a few other countries. Only works with the latest versions of Firefox, Chrome, and Safari browsers.
Before using any open-source genealogy database please make sure to investigate the organization that provides the service. We live in an age where people's data is extremely valuable, and while most of these services are altruistic in nature it is important to proceed with caution.