Sourcefiles:

gtk_base.c       - Basefunctions, boxes
gtk_label.c      - backgroundtext
gtk_button.c     - buttons, checkbox
gtk_menu.c       - menus
gtk_entry.c      - Entry
gtk_image.c      - image, button with image
gtk_dlg_files.c  - File-open/save
gtk_dlg_std.c    - msgbox dialogs slider
gtk_msgWin.c     - messagewindow
gtk_lists.c      - lists
gtk_multichoice.c- radiobuttons, popup, combo
gtk_container.c  - frame, notebook, toolbox
gtk_ed1.c        - texteditor
gtk_tree_it.c    - treeview
gtk_opengl.c     - OpenGL-window
gtk_gl_x11.c     - Gtk-binding OpenGL

gui_base.c       - internal functions
gui_gtk_ut.c     - internal functions
ut_umem.c        - internal functions
ut_umb.c         - internal functions

Examples:

hello-world.c- simple button
tst_gui1.c   - demo all widgets
tst_gui2.c   - demo all widgets
tst_lst1.c   - demo list - 1 col
tst_lst2.c   - demo list - 2 cols
tst_ed1.c    - demo texteditor

tst_gui_gl1.c    - OpenGL-functions
tst_gui_gl2.c    - OpenGL-functions

tst_trackball.c  - OpenGL-trackball
tst_surf2.c      - OpenGL-demo

Report bugs, improvements to support at gcad3d.org