HelenOS sources

root/uspace/lib/ui/src/

[..]
accel.c checkbox.c clickmatic.c control.c dummygc.c
entry.c filedialog.c filelist.c fixed.c image.c
label.c list.c menu.c menubar.c menudd.c
menuentry.c msgdialog.c paint.c pbutton.c popup.c
promptdialog.c rbutton.c resource.c scrollbar.c selectdialog.c
slider.c tab.c tabset.c testctl.c ui.c
wdecor.c window.c
[..]
HelenOS homepage, sources at GitHub