Several projects have started using XCB.

• Xlib itself has replaced Xtrans with XCB for the low-level transport layer (see XlibXcb).
• The Cairo library has an experimental XCB backend.
• Vincent Torri has worked to port evas canvas component of Enlightenment from Xlib to XCB.
• The recent MPX (multi-pointer) extension was prototyped using XCB.
• Work is ongoing to port selected default X apps from Xlib and Xt to XCB.
• awesome, a window manager, uses XCB instead of Xlib.
• Compiz requires XCB.
• Xine and the Kaffeine KDE frontend for Xine use XCB, and XCB fixed some previously unfixable threading problems.
• samurai-x, a window manager written in python. samurai-x2 uses xcb instead of Xlib.

In addition, there are a number of demos available from the XCB repository.