It is a high-performance proxy caching
server for web clients, supporting FTP, gopher, and HTTP data
objects. Unlike traditional caching software, Squid handles all
requests in a single, non-blocking, I/O-driven process.
iProxy by AT&T is a classical example of a programmable
proxy that allows accessing, caching, and processing of Web data. Besides the standards caching mechanisms, it also
offers tools for processing the HTTP data flow by writing Java classes
or writing scripts in a specifically designed script language.
Muffin is a World Wide Web filtering system written entirely in
Java that can filter any HTTP data sent and received by your web browser.
Users can write their own filters in Java using the provided filter interfaces.
An important direction toward standardization is being conducted by
the IETF Working Group for ``Open Pluggable Edge Services''
(OPES). Their goal is to define an open standard that allows
intermediaries to provide services on the data flow.