milter manager is a flexible and low administrative cost anti-spam system that can be used with MTAs that support milters like Sendmail and Postfix. It provides an effective solution by combining a range of existing milters.
OpenDKIM is a DKIM implementation with both a C library for writing your own applications and a milter-aware filter for use with recent MTAs.
A text editor aimed at developers.
An RPN calculator for the X Window system