From the author (Michael Shields <shields@tembel.org>):

ppgen generates passphrases using strings of words, long enough to have
an arbitrary level of entropy.  It can use any dictionary and the best
available source of randomness, including PGP's cryptographic RNG if you
have version 2.6.2.  It is written in portable C, and it is fairly fast.

You can use ppgen to generate passphrases whenever you have a program that
accepts long passwords.  I use it for Kerberos and for local passwords
(I use the FreeBSD MD5-based crypt(3), not the standard limited Unix one),
and for my PGP keyring.

Because ppgen is so simple, it can also easily be used by passwd(1)
or adduser(1) programs to choose passwords for users.