plugdaemon is a load-balancing "plug" proxy. It allows you to forward TCP connections to one or multiple hosts, using load balancing or failover, and to route the connections through an HTTPS proxy. Access control is done by source interface or by originating IP. Outgoing connections can be bound to a specific IP address.
Amber sits in the tcpserver chain for qmail and implements an "amber list" for incoming mail. This neither accepts nor rejects connections, but implements a number of timing-related tricks to fake out spam and virus software that doesn't implement SMTP correctly. For example, it can defer requests from new IP addresses for a few minutes before it starts passing connections on to smtpd, pause and check for programs that send data before the HELO, and otherwise make things rough for bandit bulk mailers.
Univert is a Universal Unicode Converter, at least as universal as the Unicode implementation in Tcl 8.1 or later can manage on your computer. Univert will convert interchangably between the following formats: native Tcl unicode, hex bytes or words separated by spaces, decimal bytes or words separated by spaces, HTML entities, UTF-8/URL encoding, quoted printable with whatever the current encoding is, and C string with whatever the current encoding is.