Schemaball is a flexible schema visualizer for SQL databases. The purpose of Schemaball is to help visualize the relationships between tables. Tables are related by foreign keys, which are fields which store the value of a record field from another table. Figure | A MySQL schema of our sequencing LIMS database. Schemaball produces images called schema balls. Schemaball is free software, licensed under GPL. I am not longer actively working on Schemaball. Schemaball was published in SysAdmin Magazine (Krzywinski, M. I've since been using the circular composition form in my Circos project, which applies this layout to visualizing genomes (Circos is particularly popular in the field of comparative genomes, in which relationships between two or more genomes are analyzed and displayed). Ensembl balls!
Related: Data visualisation tools