| .GAMDB00P | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .GBA | Unknown Developer | Game Files | Game Boy Advance ROM | GBAoid | Unknown Developer |
| .GEOM | Unknown Developer | Uncommon Files | AVS Application Visualization System File | Unknown Software | Unknown Developer |
| .GERMAN | Unknown Developer | Uncommon Files | Unknown Apple II Data File | Unknown Software | Unknown Developer |
| .GHI | Unknown Developer | Settings Files | NCSA Mosaic Configuration File | Unknown Software | Unknown Developer |
| .GIF_ | Unknown Developer | Uncommon Files | GIF Image Filter Databgif File | Unknown Software | Unknown Developer |
| .GKNOTE | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .GL3 | Unknown Developer | Data Files | Green Line File | Unknown Software | Unknown Developer |
| .GLJ | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .GLX | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .GOH | Geoworks Ensemble | Data Files | Geoworks GOC Header File | Unknown Software | Unknown Developer |
| .GON | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .GOV | Unknown Developer | Uncommon Files | Netmino File | Netmino | Unknown Developer |
| .GQ | Unknown Developer | Data Files | QLFC Archive Or Epson Printer Page Description Language | Unknown Software | Unknown Developer |
| .GQA | Hummingbird Ltd. | Data Files | BI/Query Data Model Admin Layer | Unknown Software | Unknown Developer |
| .GR3 | Orchid Technology KK | System Files | Graphics Device Driver | Unknown Software | Unknown Developer |
| .GRAPHICS | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .GRIP | World Meteorological Organization | Data Files | Gridded Binary File | Unknown Software | Unknown Developer |
| .GRQ | Barco Graphics | Graphic Files | Quickstep Barco Graphics File | Unknown Software | Unknown Developer |
| .GRS | Headlight Software | Settings Files | GetRight Skin | Unknown Software | Unknown Developer |
| .GS3 | GameStarter | Developer Files | GameStarter File | FPSC GameStarter | Unknown Developer |
| .GSFX | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .GSV | Mad Catz | Game Files | GameShark Saved Game | Unknown Software | Unknown Developer |
| .GSW | Unknown Developer | Spreadsheet Files | GraphShow Worksheet File | Unknown Software | Unknown Developer |
| .GWQA | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .GX1 | Unknown Developer | Graphic Files | Show Partner Graphics File | Unknown Software | Unknown Developer |
| .GYS | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .GZ0 | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .H! | Perfect world Inc. | Database Files | Perfect Database Help Database File | Unknown Software | Unknown Developer |
| .H1 | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .HAI | Unknown Developer | Uncommon Files | Ntgraph Nt09b-2b Emx Lib File | Unknown Software | Unknown Developer |
| .HARP | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .HBQ | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .HEAD | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .HEADER | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .HEB | Unknown Developer | 3D Image Files | DEcomp 3D Scene Data | DEcomp | Unknown Developer |
| .HEC | Unknown Developer | Data Files | Grafic Pvquan Quant File | Unknown Software | Unknown Developer |
| .HED | XnSoft | Graphic Files | Hi-Eddi Image File | Unknown Software | Unknown Developer |
| .HELPER | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .HER | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .HEY | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .HFI | Hewlett-Packard | Font Files | HP Font | Unknown Software | Unknown Developer |
| .HFX | Smith Micro Software | Data Files | HotFax Data File | Unknown Software | Unknown Developer |
| .HGC | Unknown Developer | Data Files | PC Fold Data | PC Fold | Unknown Developer |
| .HIGH | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .HJD | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .HLF | Eugene Roshal | Data Files | FAR Manager Help Data | Hires Interlaced | Unknown Developer |
| .HLG | BMERC | Data Files | BMERC Homolog File Format | Unknown Software | Unknown Developer |
| .HLT | Unknown Developer | Data Files | Watcher Database Trades List File | Watcher Database | Unknown Developer |
| .HLW | Unknown Developer | Data Files | Win32/AMalum.EDHZ Data | Unknown Software | Unknown Developer |
| .HM4 | Lorex Technology | Backup Files | Lorex Backup File | Unknown Software | Unknown Developer |
| .HNB | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .HNL | Unknown Developer | Data Files | Hunter MFC Data | Unknown Software | Unknown Developer |
| .HNM | Cryo Interactive Entertainment | Video Files | Cryo HNM Movie Soundtrack | Unknown Software | Unknown Developer |
| .HNQ | Unknown Developer | Uncommon Files | Hunter File | Unknown Software | Unknown Developer |
| .HNT | Unknown Developer | Uncommon Files | Hunter CSV Based Collections | Unknown Software | Unknown Developer |
| .HNY | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .HOF | Unknown Developer | Game Files | Hall Of Fame Data | Unknown Software | Unknown Developer |
| .HONMOD | S2 Games | Game Files | Heroes Of Newerth (HON) Modification Manager File | HON Modification Manager | Unknown Developer |
| .HOR | Unknown Developer | Data Files | Horoscope Data | Winhoro | Unknown Developer |
| .HOX | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .HP5 | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .HP?= | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .HPDATA | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .HPF | IBM | Developer Files | High Performance Fortran File | Fortran 90 With The pghpf Extension | Unknown Developer |
| .HPH | Unknown Developer | Uncommon Files | Designer Graphics System 2 Data File | Designer Graphics System 2 | Unknown Developer |
| .HPI | Hemera Technologies | Raster Image Files | Hemera Photo Objects Image File | HEMERA software | Unknown Developer |
| .HPRT | Apple | Data Files | Golden Orchard Apple II CD Rom File | Unknown Software | Unknown Developer |
| .HQB | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .HQM | Unknown Developer | Game Files | Hardcore Questing Mode Data File | Hardcore Questing Mode | Unknown Developer |
| .HR | Atari Corporation | Graphic Files | Atari Picture Image File | Unknown Software | Unknown Developer |
| .HRYX | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .HSM | Unknown Developer | Developer Files | Assembly Language Header File | Assembly Programming Language | Unknown Developer |
| .HUA | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .HUF | David A. Huffman | Data Files | Huffman Encoded Data | Unknown Software | Unknown Developer |
| .HVL | Unknown Developer | Audio Files | Commodore Amiga HivelyTracker Audio Module | Hively Tracker | Unknown Developer |
| .HVT | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .HVUF | Unknown Developer | Data Files | Hydraulic Calculation Format | Unknown Software | Unknown Developer |
| .HWA | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .HWK | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .HX_ | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .HYB | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .HYD | MARIN | Database Files | MARIN Hydrodynamic Database File | Unknown Software | Unknown Developer |
| .HYL | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .HZ | Unknown Developer | Text Files | Chinese (Hanzi) Text | Unknown Software | Unknown Developer |
| .HZB | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .I-E | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .I0 | Unknown Developer | Uncommon Files | Winter Windows Scheduler File | Unknown Software | Unknown Developer |
| .I3ML | Unknown Developer | Uncommon Files | I3ML Source Page | Unknown Software | Unknown Developer |
| .I66 | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .I8T | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .IA | Unknown Developer | Web Files | Internet Archive | Unknown Software | Unknown Developer |
| .IAC | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .IAE | Unknown Developer | Uncommon Files | Uncommon File Extension | Unknown Software | Unknown Developer |
| .IBJ | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .ICN | Microsoft Corporation | Raster Image Files | Windows Icon File | Unknown Software | Unknown Developer |
| .IDD | Adobe Systems Incorporated | Page Layout Files | Adobe InDesign For Mac Document | Unknown Software | Unknown Developer |
| .IDENTIFIE | Unknown Developer | Uncommon Files | Unknown File Type | Unknown Software | Unknown Developer |
| .IDK | Anville Instruments | Data Files | Interface Development Kit Data | Unknown Software | Unknown Developer |
| .IDQ | Microsoft Corporation | Data Files | Microsoft Internet Explorer Data Query File | Unknown Software | Unknown Developer |
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