RubyGems is a package manager for the Ruby programming language that provides a standard format for distributing Ruby programs and libraries (in a self-contained format called a “gem”), a tool designed to easily manage the installation of gems, and a server for distributing them. In the main you can use most of these gems in ruby-processing projects, though some built with native extensions may not be usable with jruby, there are usually good and sometimes better java alternatives (including gems built for jruby). But there’s more there are gems that have been build exclusively for use with jruby-projects, that make it even easier to use processing libraries in JRubyArt and propane. There are gems to help with maven builds, publish web-pages (jekyll and its github flavors) that are used to bring you this content etc.
Building a gem for use with JRubyArt / Propane
The arcball.gem for propane and PiCrate, is a reasonable template for producing your own standalone processing library, that can be installed as a gem. You may also found my guide to creating jruby-extensions useful if you wish to stick to the ‘jruby-extension convention’ (my extensions and those created by jruby guys are sublety different we use
implements Library, whereas proposed convention is to use
implements BasicLibraryService). You could also look at other gems built for jruby, which include more advanced features, there is no requirement to stick to convention, since both forms are likely to continue to be supported.