I use OpenGL, but I had a bad, *very* bad experience with GLUT. It crashed very often, locking up my Windows 98 (at the time), and the Linux version of GLUT just plain refused to start.

So I decided "to hell with it", and wrote my own window manager. Two window managers in fact - one for Windows, other for Linux. It was a pain, and the functionality is still very limited (for example, you cannot hide mouse pointer in current version yet, and the typing isn't implemented for Linux) - but its pluses are that
a). It's entirely in FreePascal.
b). The code size is infinitesimal (my program with the built-in window manager is only 100K in size - and that includes full OpenGL interaction, fullscreen mode switching, etc.)
c). It really doesn't require anything except gl/glu, which, you may presume, are already installed on any machine. Thus your entire installation package can be as small as 100k.

I know of one other man who built his own window manager - Michalis Kamburelis with his KambiLib. I used his code as a reference when I was researching the video mode switching under Linux.

My library
Michalis Kamburelis' Page