File with DOWNLOAD file extension usually contains an incomplete download started by Apple Safari web browser. Apple Safari adds .DOWNLOAD file extension to a file name when it starts downloading. When downloading process is done .DOWNLOAD file extension removed from the file name.

JavaScript Object Notation (JSON) is a format used to store structured data in JavaScript derived data format. JSON was designed by Douglas Crockford while his work in State Software. JSON at that time was designed to exchange application state information between web application and back-end server.

Office Open XML (also referred to as OOXML or Open XML) is an ISO/IEC standardized ZIP-compatible file format originally developed by Microsoft for representing spreadsheets, charts, presentations and word processing documents. Starting with Microsoft Office 2007, the Office Open XML file formats (ECMA-376) have become the default file format of Microsoft Office.

Office Open XML (also referred to as OOXML or Open XML) is an ISO/IEC standardized ZIP-compatible file format originally developed by Microsoft for representing spreadsheets, charts, presentations and word processing documents. Starting with Microsoft Office 2007, the Office Open XML file formats (ECMA-376) have become the default file format of Microsoft Office.

GPX is the standard file extension for the exchange and storage of map and route data on GPS devices, smartphones and computers.

A file with DXF extension (acronym for Drawing Exchange Format) is a file format for CAD design drawings that belongs to the AutoCAD program group, and is used to save the drawings created by those programs. This type of files allows interoperability between the DWG files, proprietary file format of the AutoCAD program, and the rest of the programs on the market, proprietary or license free.

CFG file extension is used by files storing various kinds of configuration information. CFG files are frequently referred to as configuration files. Configuration files can store various parameters, settings and start-up information used by applications or operating system.

PSD is a file extension used by Adobe Photoshop to store its graphics files. Adobe Photoshop is a de-facto standard in a raster image editing software. First version of Photoshop was developed in 1988 by Thomas and John Knoll. It was subsequently sold to Adobe Systems which owned it since then.

ICS file extension is used by iCalendar internet standard to store events, to-dos, free/busy information and journal entries. The ICS file format is defined in RFC-5545 specification.

EML file extension is used to store email messages in RFC-8222 format. Many applications including Outlook Express, Thunderbird, Apple Mail, Windows Mail, Postbox, and others use EML format to export and import e-mails.

Most frequent use of RAR extension is to store compressed information archived using RAR format. It is a proprietary compression format developed by Eugene Roshal. Compressing files is very useful when you want to transfer them over the internet since compression reduces amount of information to transfer. Also you may fit much more information on your PC hard drive if you compress information that you don't use.