From the product page

'NTLM Authorization Proxy Server' (APS) is a proxy software that allows you to authenticate via an MS Proxy Server using the proprietary NTLM protocol. Since version 0.9.5 APS has an ability to behave as a standalone proxy server and authenticate http clients at web servers using NTLM method. It can change arbitrary values in your client's request header so that those requests will look like they were created by MS IE. Main features:

1. supports NTLM authentication via parent proxy server (Error 407 Proxy Authentication Required);
2. supports NTLM authentication at web servers (Error 401 Access Denied/Unauthorized);
3. supports translation of NTLM scheme to standard "Basic" authentication scheme;
4. supports the HTTPS 'CONNECT' method for transparent tunnelling through parent proxy server;
5. has ability to change arbitrary values in client's request headers;
6. supports unlimited number of client connections;
7. supports connections from external hosts;
8. supports HTTP 1.1 persistent connections;
9. stores user's credentials in config file or requests password from a console during the start time;

From the project page

1. remove unwanted HTML (adverts, flash, etc.)
2. popup blocker
3. disable animated GIFs
4. filter images by size, remove banner adverts
5. compress documents on-the-fly (with gzip)
6. reduce images to low-bandwidth JPEGs
7. remove/add/modify arbitrary HTTP headers
8. configurable over web interface
9. usage of SquidGuard blacklists
10. antivirus filter module
11. detection and correction of known HTML security flaws
12. Basic, Digest and (untested) NTLM proxy authentication support
13. per-host access control
14. HTTP/1.1 support (persistent connections, pipelining)
15. HTTPS proxy CONNECT and optional SSL gateway support

From the product web-site:

SPIKE Proxy is a professional-grade tool for looking for application-level vulnerabilities in web applications. SPIKE Proxy covers the basics, such as SQL Injection and cross-site-scripting, but it's completely open Python infrastructure allows advanced users to customize it for web applications that other tools fall apart on.

Features include

1. HTTPS Man in the Middle support.
2. Archives all requests so you can edit and resend them.
3. Powerful fuzzer, crawler, and other web application auditing features
4. Can apply a regular expression to either side of the connection (useful for removing client side javascript authentication or browser checks
5. NTLM support
6. Robust and tested with many browsers and applications
7. Fully open source
8. "Recent Requests" window
9. Supports chunked encoding
10. And much more.

From the product page

Willow is a content-filtering proxy server. It bears one similarity to the many other pieces of software available for web filtering in that it is designed to filter web content. That, however, is where the similarities end. The differences between Willow and other solutions are significant, and these differences make Willow the first really usable internet filter.

In addition to being the first web filter to really work, Willow was also designed to make life easy on network administrators. To this end Willow supports the following:

• HTTPS tunneling
• response caching
• filtering based on any part of the request or response (domain, url, headers, etc.)
• through-the-web management
• authentication to a Windows NT/2000 domain
• authentication through unix password files

Amit has written a variety of proxies, with differing features. Among the features of the varying proxies are

1. Content filtering
2. Content filtering on streamed content
3. External configuration files
4. Gzip encoding
5. Chunked encoding
6. Persistent Connections
7. DNS Lookups
8. Loadable modules
9. A java applet which acts as a user interface

Among the loadable modules that come with Proxy 3 are

1. mod_proxy: provide magic URLs that display the proxy's internal state.
2. mod_stdio: listen for proxy events (HTTP connections, errors, timeouts, ad removal, etc.) and display them on stdout.
3. mod_curses: listen for proxy events and display them in a curses UI.
4. mod_gtk: listen for proxy events and display them in a GTK UI; also allow changing settings.
5. mod_ui: listen for proxy events and display them in a Java applet (not included); also allow changing settings.
6. mod_stats: listen for proxy events and display statistics when the proxy exits.
7. mod_timing: display slow DNS lookups and slow proxy filters.
8. mod_cookies: listen for cookie events (sent by server, sent by browser) and display them on stdout.
9. mod_headers: display HTTP headers (sent by server, sent by browser) on stdout.
10. mod_html: modify HTML -- change Slashdot color scheme from green to blue; rearrange My Excite portal layout; change Microsoft quotes to standard ASCII quotes; remove popup ads; remove banner ads.
11. mod_geocities: modify HTML -- remove Geocities popups.
12. mod_java: modify Java bytecode (wrap audio, thread, frame, socket objects).
13. mod_slashdot: modify images -- change Slashdot color scheme from green to blue by altering the GIF files.
14. mod_block: block clear GIFs.
15. mod_cache: cache documents forever.
16. mod_dnsprefetch: parse HTML documents, find hostnames, prefetch the DNS lookups for them so when you click on a link, the (often slow) DNS lookup is already performed.
17. mod_formdata: display form upload data.
18. mod_ignorecache: remove headers which tell the browser not to cache certain sites.
19. mod_nocookie: block servers from setting cookies.

Replicator is a replicating HTTP proxy server. Files that are downloaded through the proxy are transparently stored in a private cache, so an exact copy of accessed remote files is created on the local machine. It is in essence a general purpose proxy server, but especially suited for maintaining a cache of Debian packages.

From the product page: Here is a quick summary of WebDebug's features:

1. Written in Python, tested on Windows NT, 2000 and Solaris. Should run on most (all?) environments that Python supports. Runs best with thread support but you can turn that off
2. Records all HTTP requests and responses by acting as a browser's proxy server. Supports Keep-Alive
3. Displays these HTTP messages (including headers, content, etc.) through a simple browser interface
4. Generates statistics such as total message size, total size of each mime-type, throughput, etc.
5. Allows the saving and loading of captured HTTP requests/responses and also statistics in tab-delimited file format, suitable for importing into spreadsheets

From the product page

In a XML-configuration file you can specify python-functions as processors for the HTTP-messages you are interested in (requests or responses, which match certain criteria). You may have as many processors as you want, without modifying the actual program. The only thing you need to do, is configure the httpMonitor and write your processors.

The package comes with three sample processors. One for logging header-information of the HTTP messages (httpMonitor.filters.logger), one for modifying header fields (httpMonitor.filters.headermodifier) and a third one for accessing (and modifiying) parsed html-text. The processors can be configured to tell them exactly what to log or what to modify.

From the product page:

adzapper is a filtering proxy that can block ads from being displayed on your web browser. instead of ad banners, you see blank spaces: adzapper transforms the ads into transparent gifs.

The rules that describe what are ads and what are not ads are called "zaplets", and are configurable on a per-website basis. This way, when websites change their ads or their graphic design, it is easy to build and share new zaplets that block the ads.

adzapper is based on Sam Rushing's Medusa, a very fast asychronous-sockets web-server written in Python. Medusa is single threaded, but this doesn't mean it is slow! in my experience it is one of the fastest, lightest webservers out there.

From the product page

Alfajor is an http cookie filter, written in Python with an optional GUI. It acts as an http proxy (you must configure your browser to use it) and can either contact sites directly or work with a second proxy (eg. a cache).

The program allows cookies to be sent from your browser to any address which matches a list of regular expressions. The GUI allows the filter to be turned on and off, sites to be added or removed as they are accessed, and the list of regular expressions to be edited.

From version 1.3, Alfajor can block all data from named sites. This allows filtering of adverts. By running two instances of the program in series, cookies can be controlled and adverts blocked. For more information, see here.

Please note that Alfajor does not fully conform to any HTTP version. However, in practice, it works with the vast majority of sites.

From the product page: TCPWatch is a utility written in Python that lets you monitor forwarded TCP connections or HTTP proxy connections. It displays the sessions in a window with a history of past connections. It is useful for developing and debugging protocol implementations and web services. The latest version, 1.2, adds support for recording sessions to a directory.