The latest Chimera Mac daily build (Nov 5, 2007) works on Mac OS 10.5 Leopard (tested on Intel Mac). http://www.cgl.ucsf.edu/chimera/alpha-downloads.html Earlier Chimera versions did not start-up correctly on Leopard -- no Chimera window was displayed. The problem was that a new Leopard feature is to automatically start the X11 window server. Chimera also tries to automatically start he X11 server. When both Leopard and Chimera tried to start X11 it did not work correctly. The new Chimera code does not try to start X11.app on Leopard, letting Leopard do it. An error message is displayed in the Chimera reply log when Chimera starts on Leopard about an unprocessed Apple event. We believe this is a Python problem. It does not appear to cause any problem in Chimera operation. It will be fixed in a future release. Tom