MPresentationViewer is freeware.
The source code is released under the GPL. .NET project file included. Tested with .NET, without video should compile without too many problems on Linux.
You may find this tutorial by Christian Partl (PDF, 1.9 MB) quite useful.
CreditsWritten by Marcel Lancelle. This project started in 2002 and was written for my own presentations. Thanks to Sebastian Schuberth for 3D object loading framework and to all others providing free code or tools.