GlimmerBlocker is no longer maintained and should no longer be used as web sites have migrated from using plain http to using https (i.e. encrypted) which prohibits modification by a proxy unless you resort to install custom SSL certiticates on the client.
You should use a browser extension instead.
It was made as a hobby project during 2007-2008 by Peter Speck. It features both a custom http server and http client and a Mac OS X control panel.
GlimmerBlocker doesn't hack into Safari, so GlimmerBlocker's user interface is a System Preferences Pane instead of being part of Safari's preference window. The following images show the System Preferences Pane.
The history tab shows which URLs GlimmerBlocker has blocked or modified, and which rule that caused it. You can double-click a line to edit the rule.