Wrt is a project mainly written in D, it's free.
Real-time raytracing engine in D
Real-time raytracing in D programming language
License: LGPL version 3 or later
Author: Witold Baryluk Copyright: Witold Baryluk, 2008-2011
Note to the contributors: By doing contributions, including pull request, you give permission and right to Witold Baryluk, to eventually change license type in the future. All contributed code will remain public, and can always be forked by anyone.