Free caching software

eAccelerator
eAccelerator is a PHP accelerator derived from the MMCache extension for the PHP programming language.

MMCache
MMCache, also known as Turck MMCache, is a PHP accelerator, or an extension to PHP meant to improve performance.

nginx
nginx is a Web server and a reverse proxy server for HTTP, SMTP, POP3 and IMAP protocols, with a strong focus on high concurrency, performance and low memory usage.

PHP accelerator
A PHP accelerator is a PHP extension designed to improve the performance of software applications written in the PHP programming language.

Polipo
Polipo is a fast and lightweight, forwarding and caching proxy server, SOCKS proxy and computer software daemon.

Squid (software)
Squid is a proxy server and web cache daemon.

SquidNT
SquidNT was a port of the Squid proxy server to Microsoft's Windows NT-based operating systems.

Traffic Server
The Apache Traffic Server (TS) is a modular, high-performance reverse proxy and forward proxy server, generally comparable to Nginx and Squid.

Varnish (software)
Varnish is an HTTP accelerator designed for content-heavy dynamic web sites.

WWWOFFLE
WWWOFFLE is a proxy server and web caching software, allowing dial-up or broadband users to cache data for offline use.