Fold3 is a private, subscription-based archive service and, as such, it does not share the same open-source, not-for-profit philosophy of History Leaks. Every February, however, the site opens its Black History Collection to the huddled masses for free. Although the site focuses on military records, there are diverse sources on slavery, emancipation, and civil rights. Many of the collections consist of public domain documents scanned from the National Archives and Records Administration in Washington, DC. Users are encouraged to take advantage of this month-long offer to download as much as they can. More information can be found here.
Source: National Archives and Records Administration (Washington, DC)