GlimmerBlocker is no longer maintained and should no longer be used as web sites have migrated from using plain http to using https (i.e. encrypted) which prohibits modification by a proxy unless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 did not only block requests but also allowed for adding custom css and javascript to the pages. It also allowed for modification of the page html before the browser receives the html, which made some modifications much easier than DOM based modifications.
OBS: This is the last version of GlimmerBlocker that will support Mac OS X 10.5 as Apple does not support 10.5 any longer with their latest developer tools. Next version of GlimmerBlocker will only support 10.6 and 10.7
Fixed bug: 'request' rules are now recorded in history tab. Reported by Uwe Gansert
Minor: Fix internal javascript stringify function so it works for arrays.
Version 1.4.16 was released 2011-08-01
Release notes for 1.4.15, 1.4.14, 1.4.12, 1.4.9, 1.4.8, 1.4.7 and list of all release notes.