Several projects have started using XCB.

• Xlib itself has replaced Xtrans with XCB for the low-level transport layer (see XlibXcb).
• The http://cairographics.org/ library has an experimental XCB backend.
• Vincent Torri has worked to port evas canvas component of http://www.enlightenment.org/ 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.

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