Make your gem available on a web site for FTP site for downloading. Users can get the gem with conventional internet tools (e.g. browsers and FTP clients) and do a local install.

By running gem server on your box, you can serve your entire set of installed gems to anyone.

Further instructions TBD.

You can make a gem available for manual download.

RubyForge (http://rubyforge.org) will automatically deploy any .gem file you upload to a project download area. I encourage you to get a RubyForge account and start a RubyForge project for your code. Even if you only use the file download area, it provides a mirror for your software for when your main site goes down.