GlimmerBlocker
HTTP based ad blocker for Mac OS X
No hacks, no instability
Upgrade Safari whenever you like, no need to wait for an upgraded hack
GlimmerBlocker is no longer maintained and should no longer be used as web sites have migrated from using plain http to using https (i.e. encrypted) which prohibits modification by a proxy unless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.
The use of keep-alive/connection headers have been improved so Safari doesn't waste time trying to reuse a connection which is not reusable. In addition to being faster, this helps compatibility with some sites.
Never use keep-alive connections to Safari when downloading attachments as it seems like Cocoa's URLDownloader has a keep-alive bug when concurrently downloading several documents from the same server. The symptom is that the download hangs for a while when it is almost done (99%). This is often seen when downloading multiple items from rapidshare.
Little Snitch users: GlimmerBlocker now checks if Little Snitch must be upgraded. The 'Core System Version' 385 often breaks internet connectivity and must be upgraded to 387. Unfortunately, version 2.0.4 of Little Snitch have been released with both 385 and 387, so current 2.0.4 users may have to upgrade to 2.0.4(!). A re-download and installation of Little Snitch solves the problem.
Improved http client debug logging: Log DNS resolve time and time used for connecting to remote server.
Version 1.3.1 was released 2009-01-25. List of release notes.