appleseed is a modern, physically-based open source final frame renderer. Started in 2009, it has grown into a robust production rendering toolset and has been battle-tested on several projects such as TV documentaries, ads, promotional videos and animation shorts. appleseed is the successor to toxic, an early open source global illumination renderer first released in 2003.
appleseed is available under the MIT license.
More information at http://appleseedhq.net/.
Check out our detailed build instructions to build appleseed from source.
More developer documentation can be found in the wiki.