GlimmerBlocker is no longer maintained and should no longer be used as web sites have migrated from using plain http to using https (i.e. encrypted) which prohibits modification by a proxy unless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.
Fix problem with reactivation of GlimmerBlocker: "can't connect to host" dialog. Reported by John B. Matthews and others.
Fix problem with "Last update: (date)" that didn't get updated. Reported by David Brown.
Version 1.4.15 was released 2011-07-17
Release notes for 1.4.14, 1.4.12, 1.4.9, 1.4.8, 1.4.7 and list of all release notes.