KeyMan is a program for managing relationships of trust, remembering decisions on trust, and conveying these decisions to other people. It comes as a set of perl modules, and some front ends to these perl modules.
KeyMan has a GUI tool which allows you to do all of the operations that you might need to do on KeyMan objects. It also comes with a full set of command-line utilities that are useful for incorporating in scripts.
KeyMan requires GnuPG to be installed.
A quick guide to using the KeyMan GUI is here.