The National Museum was looted during Chad's civil wars but has since reopened with a reduced collection. Displays include artifacts from the Sao civilization, which flourished around Lake Chad from the 6th century, along with traditional crafts and archaeological finds from the Saharan north. It is a small museum and won't take more than an hour, but it provides useful background before heading into the country.
National Museum
Sao civilization artifacts and Saharan archaeology