Mac OS X 10.5+ (10.4 is no longer supported)
pcre (specifically, the C++ wrapper for pcre)
ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/
You can mount procfs as:
$ sudo mkdir /proc $ sudo chown root:admin /proc $ sudo ./procfs /proc -f
For certain things to work (and not crash procfs), you must either run procfs foregrounded (through the -f option), or use the procfs.plist file to run procfs through launchd.