Files ending in CFML are source code files in the ColdFusion Markup Language. ColdFusion ML is a scripting language developed by Allaire (now part of Adobe) for server-side Internet applications. Typically, CFML files are web pages with Coldfusion script code that runs on a Coldfusion server. The html code is added to the file by the server so that it can be displayed to the user in a web browser.
Coldfusion offers the developer a variety of functions and tags such as database queries, image manipulation and mathematical operation as well as formatting options. Coldfusion Server is few because of Adobe's proprietary license. Railo also has an open source server, but it does not support all of Coldfusion's features and tags.
CFML files are just text files that can be processed by a ColdFusion Server. They can be opened and edited in any text editor, however it is recommended to use editors with developer functions such as syntax highlighting for easier work.
A more common extension for CFML files is cfm.
The IDE Eclipse needs the extension CFEclipse to work with these files.