the current release of rebol core does not run on the 10.2 version of os x. but there is a work-around.

setenv DYLD_INSERT_LIBRARIES /usr/lib/libtermcap.dylib

update: bad news, the work-around does not work – at least with my installation...

update of the update: actually, it does work – if you put it into the .cshrc file of your home directory (i've tried it with .login).