ipredirectd has functionality similar to netcat but with some extra features. Multiple clients and full logging of network traffic are supported. It can also manipulate incoming and outgoing text traffic. Manipulation is based on pattern files that support regular expressions. This feature is probably most useful with HTTP. The software is smart enough not to apply regular expressions on non-HTML data by reading the content-type header. One possible usage is redistribution of pre-authenticated Web pages in foreign domains by replicating authentication and session cookies.
PRADS is a "Passive Real-time Asset Detection System". It passively listens to network traffic and gathers information on hosts and services it sees. This information can be used to map your network, letting you know what services and hosts are alive and used. It can also be used together with your favorite IDS/IPS setup for "event to host/service" correlation. It can help you make sure that your inventory database is up to date. PRADS commes in two versions. One written in Perl, and one written in C. Some features might only be found in one of the versions.