Open Tool Kit (Otk) is a portable widget library for making
graphical user interfaces for C programs. It
emphasizes simplicity for the application
programmer without eliminating capability. Based
on OpenGL, Otk supports Linux, Unix, and other OSs
neutrally and efficiently. It is simple and
compact, and it strives for easy compilation and
linking to other applications. In seeking to
address several issues associated with earlier
graphics APIs, Otk explores some interesting
methods, such as window-relative layout instead of
pixel-based layout.