It's hard to write about this latest family history database, as it's such a grim and awful reminder of humanity at its worst. Still, the Shoah Victims' Names Database at Yad Vashem is an incredible source of information on the millions of people who died at the hands of the Nazis during the holocaust.
The database contains about 3 million names, and hopes to one day have a fuller accounting of all the victims of Hitler's attempted genocide. The database is almost exclusively focused on Jewish names from all over Europe, though I understand there are records of non-Jews included as well.
Read the story of how Rozel and Kayla were identified from their photo.
The search interface looks to be very well designed, and will pull up records of closely related spellings and pronounciations for the name you search on. The information in the records varies, but the designers have bent over backwards to include as much information as they possibly can, including parents, siblings, relatives, and information on where and how people lived.
There is a substantial and poignant photo archive at the site.
You can also search the Related Lists Database. This resource is not searchable by individual names, but can be browsed by place name, group identity, or general keyword search. There are probably hundreds of thousands of individuals named on these lists that haven't yet been entered into the master Shoah Victims' Names Database.
Visit the main page of Free Genealogy Tools for more, umm, free genealogical tools.
And don't forget to also check for your family history at Ancestry.com and NewspaperArchive.com. These are subscription databases, but they are among the most powerful research tools available for looking into family roots.