Nginx is a web server, which can also be used as a reverse proxy, load balancer and HTTP cache.

Squid is a caching and forwarding HTTP web proxy. It has a wide variety of uses, from speeding up a web server by caching repeated requests.

Varnish is an HTTP cache.

Internet Archive is a nonprofit digital library which stores a copy of millions of web page history.

PrimoCache is a supplementary software caching scheme to improve the system performance.

eBoostr application allows you to use an additional drive (flash memory or hard disk) or free RAM as another layer of performance-boosting cache.