Complex sentence: It is being developed for modern Unix-like operating systems, including Linux, Mac OS X, and Solaris--in general, any OS that conforms to POSIX and has a working implementation of the GNU Autotools.
Split into simpler sentences: It is being developed for modern Unix-like operating systems, including Linux, Mac OS X, and Solaris. Specifically, any OS that conforms to POSIX and has a working implementation of the GNU Autotools.