The Irrlicht Engine is an open source high performance realtime 3D engine written and usable in C++. It is completely cross-platform, using D3D, OpenGL and its own software renderers.
db4o is the world's leading open source object database for Java and .NET. Leverage fast native object persistence, ACID transactions, query-by-example, S.O.D.A object query API, automatic class schema evolution, small size (http://developer.db4o.com)