I do rather enjoy hacking in Ruby, and I'm actually developing some classes and such that might be useful to others.
This is both a class and a command-line utility for waking up a sleeping computer from another machine on the network. The standard that enables this is called Wake On LAN (WOL).
You can download the latest version here: wakeonlan.rb-0.2.1.tar.gz. This class is distributed under the GPL.
Documentation will be forthcoming. For now, the source should be understandable enough.
There is another Ruby implementation of a Wake On LAN tool available here. My implementation is not based on that code in any way. I drew inspiration and a few implementation details from the Perl wakeonlan script maintained by José Pedro Oliveira. He has also written a Wake On LAN mini-HOWTO which merits some study. I intend to make wakeonlan.rb compatible with the Perl implementation in command-line switches and file format, but there are also some extensions that I'd like to implement (e.g. arbitrary labels for host addresses in the input file).
This class enables an object to broadcast a notification that an event occurred to other objects, without having any knowledge of the objects that it is broadcasting to. An object posts a notification (identified by a string and possibly an associated object) to a NotificationCenter (generally the default one). The NotificationCenter then takes care of sending the notification to all of the objects that have registered to receive it.
You can download the latest version (0.1) here: NotificationCenter-0.1.tar.gz. This class is distributed under the GPL.
Documentation is also available, and is included in the package.
UPDATE 2004.09.30: I haven't worked on this in a while, and I haven't tested it or analyzed it for thread safety. If anyone would like to contribute a patch, I'd gladly accept it. I don't anticipate working on it any further in the near future though.