Quicken Files Extensions - What are quicken files and how do I open a quicken file?

What are quicken files and how do I open a quicken file?

File Type Category File Format
.qdf Quicken Files Quicken Data File
.qf Quicken Files Qompose Web Page Template
.qxf Quicken Files Quicken Essentials for Mac Exchange File
.zdb Quicken Files Zimbra Database File