Scilab under Mac OS X
While the Mac is not a "supported platform", Scilab works quite well in Mac OS X.
The main problem is that X11, the old X-windows system, must be installed. X11 comes with the Mac OS X disks but is often not installed by default.
X11 programs tend to work with a different look and feel then the usual Mac OS system. The most notable differences are mouse focus and mouse buttons.
The default X11 mouse focus is "focus follows mouse", that is the mouse must be in the window you want to type. The default X11 mouse has 3 buttons.
You can find MacOs X 10.4 version here : http://www.lmac.utc.fr/~mottelet/Darwin/