PHPresolver is a DNS resolver library written in pure PHP. It may help you code email address validity verification under the Win32/BeOS port of PHP because the current version has no support for DNS-related functions such as getmxrr() or checkdnsrr(). In addition, the library partially supports IPv6 address resolution.
pamtester is a tiny utility program to test the pluggable authentication modules (PAM) facility. While specifically designed to help PAM module authors to test their own modules, it might also be handy for system administrators interested in building a centralized authentication system using common standards such as NIS, SASL, and LDAP.