File extensions start with character '#'
| File Type | Category | File Format | |
|---|---|---|---|
| .!bt | Partially Downloaded Files | BitTorrent Incomplete Download File | |
| .!ut | Partially Downloaded Files | uTorrent Incomplete Download | |
| .0 | Multiple Use Files | Hacha Split Archive File | |
| .000 | Multiple Use Files | Windows CE Installation Data File | |
| .001 | Backup Files | Split Archive File | |
| .001 | Raster Graphics Files | Fax File | |
| .002 | Backup Files | Split Archive Part 2 File | |
| .0xe | Program Execution Files | F-Secure Renamed Virus File | |
| .1 | Multiple Use Files | Unix Section 1 Man Page | |
| .123dx | CAD Files | 123D Design Model File | |
| .1pe | Data Files | TurboTax Form File | |
| .1ph | Data Files | TurboTax File | |
| .1st | Text Files | Readme File | |
| .264 | Digital Video Files | Ripped Video Data File | |
| .386 | Windows Device Driver Files | Windows Virtual Device Driver | |
| .3dm | 3D Files | Rhino 3D Model | |
| .3dr | Data Files | 3DMark Results File | |
| .3ds | 3D Graphics Files | 3D Studio Scene | |
| .3dt | Data Files | 3D Topicscape File | |
| .3ga | Audio Files | 3GPP Audio File | |
| .3gp | Digital Video Files | 3GPP Multimedia File | |
| .3me | Data Files | TurboTax Form File | |
| .3pe | Data Files | TurboTax 2008 Form File | |
| .411 | Raster Graphics Files | Mavica Thumbnail Image | |
| .4db | Development Files | 4th Dimension Database Structure File | |
| .4dd | Database Files | 4th Dimension Database Data File | |
| .4dv | 4D File Format Files | 4D View Ultrasound File | |
| .4mp | Audio Files | 4-MP3 Database File | |
| .555 | Settings Files | Black & White Weather Settings File | |
| .669 | Audio Files | UNIS Composer 669 Module | |
| .6cm | Audio Files | Six Channel Module | |
| .7z | Compressed Files | 7-Zip Compressed File | |
| .8ba | Adobe Plug-in Files | Photoshop Plug-in | |
| .8bf | Adobe Plug-in Files | Filter Factory Image Filter | |
| .8bi | Adobe Plug-in Files | Photoshop Plug-in | |
| .8cm | Audio Files | Eight Channel Module | |
| .8xg | Data Files | TI-83/84 Plus Group File | |
| .8xk | Data Files | TI-83 Plus Application Upgrade File | |
| .8xs | Data Files | TI-83/84 Plus String File | |
| .8xv | Data Files | TI-83/84 Plus Variable File |