LEPL is a recursive descent parser library written in Python. It is based on parser combinator libraries popular in functional programming, but also exploits Python language features. Operators provide a friendly syntax, and the consistent use of generators supports full backtracking and resource management. Backtracking implies that a wide variety of grammars are supported; appropriate memoisation ensures that even left-recursive grammars terminate.
xtee (cross-tee/expanded tee) is a program for building complex pipelines. It resembles the tee command, except that instead of copying stdin to stdout, it copies an input file to stdout and stdin to an output file. You can use xtee for building things like a bidirectional HTTP filter (using netcat and sed).
DynaStop is a utility to examine IPv4 based addresses for Exim and procmail for the purpose of filtering based upon patterns defined by the administrator. This can be a pivotal factor in email filtering and server load management, since dynamic IP addresses are typically used for dial-up, DHCP, and DSL accounts. All of which have a designated mail exchange server through which all outbound mail flows as defined with many, if not most, large Internet service providers.
Stream Replace replaces binary data in streams (from stdin to stdout). It has two parameters: you pass a string that should literally match, and the replacement string. On stdout, every occurrence will be replaced, byte by byte. It does a job 'sed' usually cannot do: change non-text files.
a2pdf converts plain (ASCII) text files to documents in the PDF format. Its features include optional line/page numbering, multiple font support, syntax highlighting for Perl source code, and customizable headers and footers. Binaries are available for Linux x86, Mac OS X (Intel), and Microsoft Windows platforms.
Units-filter is a basic standalone filter written in C, flex, and bison. It inputs strings like "1.5e3 nN.m.s^-1" (which could be the time growth ratio of a torque) and outputs the value in standard SI units, followed by the physical dimension of this value. This parser can be embedded in educational test systems, in order to analyze a student's answer to a problem of physics or chemistry.