Dateutils are a bunch of tools that revolve around fiddling with dates and times in the command line, with a strong focus on use cases that arise when dealing with large amounts of financial data. Their target market is shell scripts that need date calculations or calendar conversions, and as such they are highly pipe-able and modeled after their well-known cousins (e.g. dtest vs. test, or dgrep vs. grep).
yuck is a command line option parser for C that works on a minimal set of dependencies---only a C compiler and the m4 macro processor are required. It supports all the standard use cases: GNU-style long options (--option), condensable short options (-xab for -x -a -b), and optional arguments to long and short options (--foo[=BAR]), multiple occurrence of options (-vvv). Most importantly, it does not depend on libc's getopt() nor getopt_long().
Password management belongs to the command line. Deep into the Unix heartland, the shell. With Steel your passwords are safe. Steel uses RIJNDAEL encryption in CFB mode with 256 bit keys. Steel is simple, Steel is advanced, Steel is adaptable. Steel is the new prophet of password management
libcfg+ is a C library that features multi- command line and configuration file parsing. It is possible to set up various special properties such as quoting characters, deliminator strings, file comment prefixes, multi-line postfixes, and more. It supports many data types such as booleans, integers, decimal numbers, strings with many additional data type flags (such as multiple values for a single option).
termsql converts text from stdin or any file into an SQLite database table and allows users to execute SQL queries on that table, all in just one line on the command line. It can be used to sort, display, convert, extract, and modify data on the command line using syntax familiar to those who know SQL.
TunnelIt is a simple tool that uses the TUN/TAP driver to tunnel Ethernet networks over IP connections. Its simple command line interface is meant to resemble "netcat" where it is logical to do so.