mod_pagespeed improves web page latency by changing the resources on that web page to implement web performance best practices. Each sort of change that mod_pagespeed makes is embodied in a filter. The filters are run in a pre-defined order, but can be enabled and disabled in the Apache configuration file. Here is the list of filters from Google.
Interesting, that many of the tasks could be solved for Java servers (e.g. Tomcat) with the help of controls from Coldbeans. Just a few of examples:
- Extend Cache - Public cache filter
- Collapse Whitespace and remove comments - Trim filter
- embed image via Data URI: Embed Image taglib
etc. Check out more at Coldbeans site