OpenLink Virtuoso (Product Blog)
Blog Summary
See the Lite: Embeddable/Background Virtuoso starts at 25MB
Short Recap of Virtuoso Basics (#3 of 5)
Compare & Contrast: Oracle Heterogeneous Services (HSODBC, DG4ODBC) vs Virtuoso's Virtual Database Layer
Compare & Contrast: SQL Server's Linked Server vs Virtuoso's Virtual Database Layer