These a not prerequisites for the general Free Electron build to run, but rather the prerequisites for what you need to install if you want any particular Free Electron module to be built.

To build doxygen pages, xfig should be installed.

xfig, jfig, and fig2dev (for documentation)

For other technologies, see the specific "Installation Notes" for each module you wish to use.

Alembic File Format

Arnold Ray Tracer Support

Boost

FBX File Format

OpenGL Extension Wrangler Library

Native Window Implementation

OpenAL Audio Integration

OpenCL Support

OpenGL Drawing

OpenIL Raster Integration

OpenImageIO Raster Integration

OpenSubdiv Support

OpenSceneGraph Support

Perl Compatible Regular Expressions

Ptex Polygon Textures

Simple DirectMedia Layer Integration

Thread Building Blocks

TIFF Image Support

Universal Scene Description

Voxel Data Base