pkg++ is a tool to build packages. The goal is to provide a tool you can use to build a package from a generic recipe on your distribution/OS and for your native package manager. The recipes, when done correctly, can be used on multiple OSes, and thus users can share them even if they do not use the same distribution. It is as much a way to easily package as it is a way to create multi-OS package recipes repositories.
slkbuild is a script inspired by makepkg from Arch that greatly simplifies the package building process in Slackware and derivatives. It parses an easy-to-create SLKBUILD meta-file and from that creates a conventional build script that follows all of the Slackware packaging standards and that can be run on its own. The advantage of using slkbuild is that it ensures package uniformity and allows for an easy-to-edit meta-file in the event that one might require customization or might need to update the script for new releases. It also makes the build process much quicker, since it takes care of downloading the source, untarring, gzipping man and info pages, stripping binaries, making sure that the menu entry for a graphical application is compliant, as well as a host of other things.
PPM-Make is a Perl module that automates some of the steps needed to make a ppm (Perl Package Manager) package from a CPAN distribution. It attempts to fill in the ABSTRACT and AUTHOR attributes of Makefile.PL if these are not supplied, and also generates HTML documentation. ppm is used in the ActivePerl distribution. ActivePerl is primarily used on Windows and by corporations on other OSes.
GiftWrap helps you in creating Ubuntu .deb packages by guiding you through the process with minimal fuss and maximum automation. It also aims to help you in creating high-quality packages by helping you fill in as much of the package meta-information as possible, either by automatically detecting or explaining the options in an easy to understand manner. The interface aims to be clean and easy to understand (HIG 2.2 compliant) and development-friendly with well-documented code (to be done in the near future) and a roadmap.