HelenOS sources

root/uspace/lib/ui/include/ui/

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