[Argorak]

The source downloaded from the authors page[1] lists the following modification times:

    [ skade sl ] ls -la *
    -rw-r--r-- 1 skade staff  331 Jul 22  1998 Makefile
    -rw-r--r-- 1 skade staff  417 Jul 22  1998 README
    -rw-r--r-- 1 skade staff  689 Jan 18  1994 sl.1
    -rw-r--r-- 1 skade staff 7.0K Jul 22  1998 sl.c
    -rw-r--r-- 1 skade staff 4.1K Jan 18  1994 sl.h
    -rw-r--r-- 1 skade staff  980 Jan 18  1994 sl.txt

So, it is almost 20 years old.

[1] http://www.tkl.iis.u-tokyo.ac.jp/~toyoda/index_e.html