Data Structures
Here are the data structures with brief descriptions:

FTBBox | FTBBox is a convenience class for handling bounding boxes
FTBitmapFont | FTBitmapFont is a specialisation of the FTFont class for handling Bitmap fonts
FTBitmapGlyph | FTBitmapGlyph is a specialisation of FTGlyph for creating bitmaps
FTBuffer | FTBuffer is a helper class for pixel buffers
FTBufferFont | FTBufferFont is a specialisation of the FTFont class for handling memory buffer fonts
FTBufferGlyph | FTBufferGlyph is a specialisation of FTGlyph for memory buffer rendering
FTExtrudeFont | FTExtrudeFont is a specialisation of the FTFont class for handling extruded Polygon fonts
FTExtrudeGlyph | FTExtrudeGlyph is a specialisation of FTGlyph for creating tessellated extruded polygon glyphs
FTFont | FTFont is the public interface for the FTGL library
FTGlyph | FTGlyph is the base class for FTGL glyphs
FTLayout | FTLayout is the interface for layout managers that render text
FTLibrary | FTLibrary class is the global accessor for the Freetype library
FTOutlineFont | FTOutlineFont is a specialisation of the FTFont class for handling Vector Outline fonts
FTOutlineGlyph | FTOutlineGlyph is a specialisation of FTGlyph for creating outlines
FTPixmapFont | FTPixmapFont is a specialisation of the FTFont class for handling Pixmap (Grey Scale) fonts
FTPixmapGlyph | FTPixmapGlyph is a specialisation of FTGlyph for creating pixmaps
FTPoint | FTPoint class is a basic 3-dimensional point or vector
FTPolygonFont | FTPolygonFont is a specialisation of the FTFont class for handling tesselated Polygon Mesh fonts
FTPolygonGlyph | FTPolygonGlyph is a specialisation of FTGlyph for creating tessellated polygon glyphs
FTSimpleLayout | FTSimpleLayout is a specialisation of FTLayout for simple text boxes
FTTextureFont | FTTextureFont is a specialisation of the FTFont class for handling Texture mapped fonts
FTTextureGlyph | FTTextureGlyph is a specialisation of FTGlyph for creating texture glyphs
FTTriangleExtractorFont | FTPolygonFont is a specialisation of the FTFont class for handling tesselated Polygon Mesh fonts
FTTriangleExtractorGlyph | FTPolygonGlyph is a specialisation of FTGlyph for creating tessellated polygon glyphs