* expat or libxml2 - XML parsers (expat is preferred, because its API provides better error output during parsing).
* gtkmm elegant C++ wrapping for the GTK2 graphical user interface toolkit (gtkmm 2.4 required).
* gtkglext - a binding between GTK2 and OpenGL.
* OpenGL / GLU - portable, hardware accelerated 3D graphics.
* libsigc++ - type-safe C++ callback system (libsigc++ 2.0 required for gtkmm 2.4)

Optimal:
* FreeType 2 - text plugin.
* PLIB - 3D file import / export plugin.
* Python - Python scripting engine.
* Ruby - Ruby scripting engine.
* Open Dynamics Engine - physical simulation plugin.
* OpenEXR - writing high-dynamic range images.
* LibTIFF - writing TIFF images.
* ImageMagick - writing whole range of image formats (recomended).
* Graphviz - Graph Visualization Softwate
* xsltproc
* GTS - GNU Triangulated Surface library