Overview

There are a few typical difficulties that can cause your site to perform slowly.

The majority of slow-loading websites are database-driven. Unless you have caching enabled for this site server, database content is not kept on the web server. If no caching is enabled, the communication between the web server and the database server creates content dynamically for each visitor.
Concrete CMS software.
Cache & Speed Settings in Concrete CMS software.
Caching Overview of Caching
Drupal
Drupal
Article about Drupal Community caching, speed, and performance
“Boost” is a Drupal caching module.
Joomla
10 ways to boost your performance
10 Ways to Increase Your Speed Joomla
MediaWiki
Performance tuning for MediaWiki
File cache for MediaWiki
MODx Evolution
MODX may be made to fly in seven different ways.
phpBB
Overview of the phpBB Cache
phpBB cache is being cleared.
WordPress
WordPress articles about WordPress optimization
Zen Cart performance optimization
Optimizing a private server
Many of the suggestions on this page can be applied to private servers, however, for VPS-specific advice, see the PS Optimization and VPS Troubleshooting pages.

Also also