Postgrey is a Postfix policy server that implements greylisting. When a request for mail delivery is received by Postfix via SMTP, the triplet CLIENT_IP / SENDER / RECIPIENT is built. If it is the first time that this triplet is seen, or if the triplet was first seen less than 10 minutes ago, then the mail gets rejected with a temporary error. Hopefully, spammers or viruses will not try again later, even though such behavior is required per RFC.
Luit is a filter that can be run between an arbitrary application and a UTF-8 terminal emulator. It will convert application output from the locale's encoding into UTF-8, and convert terminal input from UTF-8 into the locale's encoding. It is mainly used to support xterm.