Limit the web access for some users to a list of accepted/well known web servers and/or URLs only.

Block access to some listed or blacklisted web servers and/or URLs for specific users.

Block access to URLs matching a list of regular expressions or words for specific users.

Enforce the use of domain names/prohibit the use of IP address in URLs.

Redirect blocked URLs to an "intelligent" CGI based info page.

Redirect an unregistered user to a registration form.

Redirect popular downloads like Netscape, MSIE etc. to local copies.

Redirect banners to an empty GIF.

Have different access rules based on time of day, day of the week, date etc.

Have different rules for different user groups.

and much more.....

Filter/censor/edit text inside documents

Filter/censor/edit embedded scripting languages like JavaScript or VBscript inside HTML.