FormValidator is a Ruby port of Perl's Data::FormValidator library. It makes it easy to validate data coming in from HTML forms by providing a robust set of methods to handle required fields, dependent fields, filtering, constraints, tainting, and defaults. Its modular design allows you to easily add your own filters and constraints and also lets you to keep validation data outside of your CGI scripts.
Daemonize is a Ruby module derived from Perl's Proc:: Daemon module. It allows you to easily modify any existing Ruby program to run as a daemon. Converting a program to a daemon by hand is a relatively simple process; however, this module will save you the effort of repeatedly looking up the procedure, and it will also ensure that your programs are daemonized in the safest and most correct fashion possible.
Rant is a flexible build tool. The equivalent to a Makefile for make is the Rantfile, which is actually a valid Ruby script that is read in by the rant command. It currently features automated testing, packaging, and RDoc generation for Ruby applications and libraries, creation of gzipped tar and zip archives on all supported platforms without additional software, recognition of file changes based on MD5 checksums, dependency checking for C/C++ source files (makedepend is not required), and more. It can generate a script tailored to the needs of a specific project, which can be used instead of an Rant installation so that users aren't dependent on Rant.