You can clone with
HTTPS or Subversion.
Depending on your operating system and programming language, please refer to the appropriate pages from the side bar.
Since Ruby is not a compiled language, it may not be obvious how to release games written in it to the public. For instructions see either Ruby Packaging on OS X or Ruby Packaging on Windows.
There are many games you can take a look at in the Gosu Showcase board, and even more useful libraries to use with Gosu in the Extending Gosu board!