Improve the real or perceived speed of the site, or monitor performance metrics.
"The longer a piece of content goes without being modified, the longer its cache should be." Here is the basic idea for this module.
A cache backend wrapper which lets you specify multiple cache backends in order of preference.
Keep Frontend DRY; sprinkle it with Magic
Share sessions between different domains! Not just sub-domain.
Role execution time limit is a small module that allow you to set PHP max execution time per role and command line usage(drush).