Cleanwriter is a tool for "compiling" xhtml pages from a more abstracted source. The source contains a high level markup language (some aspects of which are similar to markdown) and the cleanwriter compiler converts this to valid xhtml using a set of rules and macros.
The program is particularly useful when a large quantity of documents need to be maintained on a website. By separating the content of the documents from detailed generation of HTML and CSS tags, the documents can be made consistent and managed with ease.
Cleanwriter is currently at version 1.45 release, and is available as source or binaries.