Countdown: 4

Calling outside World can be achieved using dynamic linked libraries:

CPU Time Inquiry under OS X:
w> libc: load/library %/usr/lib/libc.dylib
w> clock: make routine! [libc "clock" sint]

Now CLOCK can be used like any other World function:
w> do [
    t: clock
    add 2 2
    clock - t
== 11

Get a SVID Random Number under Linux:
w> libc: load/library %/lib/i386-linux-gnu/
w> drand48: make routine! [libc "drand48" double]
w> drand48
== 3.907985046680551e-14

Write a string to stdout under Windows:
w> msvcrt: load/library %msvcrt.dll
w> puts: make routine! [msvcrt "puts" [[string!] pointer] uint]
w> puts "Hello, World!"
Hello, World!

The system can also be called:

Under OS X:
w> call "open"

Under Linux:
w> call "xdg-open"

Under Windows:
w> call "start"