Annotation Cold Fusion is a web development tool used to build complex, interactive web sites. It has become the tool of choice for web developers integrating back end corporate databases into their web sites. Cold Fusion consists of three primary elements: a web application server, a development environment, and a server side markup language. Cold Fusion's chief competitor is Visual InterDev with whom it has competed very successfully to date. Cold Fusion 4 is a new version scheduled for release in late 1998 or early 1999.