XLS is a proprietary binary file format called Binary Interchange File Format (BIFF) as its primary format used by Excel to store spreadsheet information. Excel 2007 uses Office Open XML as its primary file format, an XML-based container similar in design to XML-based format called XML Spreadsheet (XMLSS), first introduced in Excel 2002.

EXE is a file format of windows executable file. All executable files in Windows operating system are store in EXE format. Be careful when running EXE files receivied from unverified source since they can contain viruses

MKV file extension is used for files in Matroska multimedia container format. Matroska file format was created in 2002 based on the Multimedia Container Format. Matroska format and MKV file is widely popular storage format for multimedia files on the internet.

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.

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.

APK extension is used to deliver and install application software and middleware onto Google Android system. APK file contains compiled Android application code and all resources which are required by this code.

PART extension is used by Mozilla Firefox to store partially downloaded files. Usually this file extension is given to files which are currently being downloaded. If you see PART files on your computer it means that either Firefox Mozilla is currently downloading something or that download failed in the middle.

Direct Access Archive, or DAA, is a proprietary file format developed by PowerISO Computing for disk image files which supports features such as compression, password protection, and splitting to multiple volumes. It can be handled like a file just like other formats, such as an ISO image and BIN, but is currently only usable by PowerISO software. Popular disk image mounting programs such as Alcohol 120% and Daemon Tools currently do not support the mounting of DAA images.

KML files are very often distributed as KMZ files, which are zipped KML files with a .kmz extension. When a KMZ file is unzipped, a single doc.kml is found along with any overlay and icon images referenced in the KML.

CRDOWNLOAD is chrome partially downloaded file. Usually such file cannot be recovered since only part of it was downloaded. You need to visit website with download again and re-download it.