Apptitle ?

Assuming OSX uses the XLib, then I suspect that XStoreName will be the answer, I really need to sort my system out and install linux so I can test it there. (either that or someone else with linux could test it in the meantime?).

*EDIT*

at a guess, you would do the following:
use the same stuff in the bmx source, but update it to reflect the changes in the conditionals
Then make some changes to the C source (for linux, blitzgl.linux.c)
below:

	window=XCreateWindow(
		display,
		RootWindow(display,screen),
		0,
		0,
		width,height,
		0,
		vizinfo->depth,
		InputOutput,
		vizinfo->visual,
		CWBorderPixel|CWColormap|CWEventMask|CWOverrideRedirect,
		&swa
	);

put something like:

XStoreName(display,window,appTitle);