| .G1M | Casio Computer Co., Ltd. | Developer Files | Casio Model 9860 BASIC Program File | Unknown Software | Unknown Developer |
| .GAB | Open Source | Developer Files | Dencom Global Address Book Export File | Dencom Global Address Book | Open Source |
| .GAR | GIANTS Software | Developer Files | Farming Simulator Game Archive File | Farming Simulator | GIANTS Software |
| .GAS | Atari Corporation | Developer Files | Atari Jaguar GPU Assembly Source | Atari Jaguar | Atari Corporation |
| .GBAP | Dream Design Entertainment Software | Developer Files | GLBasic Project File | GLBasic | Dream Design Entertainment Software |
| .GBL | Ucamco | Developer Files | Gerber Bottom Layer Data File | CadSoft EAGLE | Autodesk, Inc. |
| .GDT | Open Source | Developer Files | Gretl Data File | gretl | Open Source |
| .GED | Thoughtful Creations | Developer Files | GEDCOM Genealogy Data File | Ages! | Jörn Daub e.K. |
| .GEM | RubyGems.org | Developer Files | RubyGems Package | RubyGems | RubyGems.org |
| .GFO | Oracle Corporation | Developer Files | Grammatical Framework | Java | Oracle Corporation |
| .GLADE | Open Source | Developer Files | Glade Project File | Glade | Open Source |
| .GLD | Microchip Technology Inc. | Developer Files | MPLAB C Compiler Linker Script File | MPLAB IDE | Microchip Technology Inc. |
| .GLF | Vladimir Romanyuk | Developer Files | Space Engine Shader File | Space Engine | Vladimir Romanyuk |
| .GLS | Babylon Software Ltd. | Developer Files | Babylon Glossary File | Babylon | Babylon Software Ltd. |
| .GM | GameMonkey | Developer Files | GameMonkey Script | Microsoft Notepad | Microsoft Corporation |
| .GM6 | YoYo Games | Developer Files | GameMaker 6 Project File | GameMaker Studio | YoYo Games |
| .GMD | YoYo Games | Developer Files | Game Maker Program Code | GameMaker Studio | YoYo Games |
| .GMK | YoYo Games | Developer Files | Game Maker Project File | GameMaker Studio | YoYo Games |
| .GML | Galdos Systems, Inc. | Developer Files | Geography Markup Language File | Canvas X | ACD Systems |
| .GMO | GNU Operating System | Developer Files | GNU Machine Object File | GNU gettext | GNU Operating System |
| .GMX | YoYo Games | Developer Files | GameMaker File | GameMaker Studio | YoYo Games |
| .GNI | American Advantech Corporation | Developer Files | VisiDAQ | VisiDAQ | American Advantech Corporation |
| .GNT | Micro Focus International plc | Developer Files | Micro Focus COBOL Generated Code | Visual COBOL | Micro Focus International plc |
| .GO | Google | Developer Files | Go Source Code File | MacroMates TextMate | MacroMates |
| .GOBJ | Geoworks Ensemble | Developer Files | Geoworks Object Code File | Breadbox Office | Breadbox Computer Company |
| .GP | Sublime HQ Pty Ltd | Developer Files | Gofer Project Source | Notepad++ | Don Ho |
| .GPI | Garmin | Developer Files | Garmin Point Of Interest File | Garmin POI loader | Garmin |
| .GPJ | Green Hills Software | Developer Files | MULTI IDE Project File | Green Hills MULTI IDE | Green Hills Software |
| .GR | Geosoft | Developer Files | GX Resource Source File | Oasis montaj | Geosoft |
| .GRADLE | Google | Developer Files | Android Studio Build Data | Android Studio | Google |
| .GROOVY | VMware | Developer Files | Groovy Source Code File | MacroMates TextMate | MacroMates |
| .GRXML | Sublime HQ Pty Ltd | Developer Files | Grammar Data | Sublime Text | Sublime HQ Pty Ltd |
| .GS | Google | Developer Files | Google Apps Script | Google Apps Script | Google |
| .GS3 | GameStarter | Developer Files | GameStarter File | FPSC GameStarter | Unknown Developer |
| .GSS | McGraw-Hill Education | Developer Files | Geometer's Sketchpad Script | Key Curriculum Press Geometer's Sketchpad | McGraw-Hill Education |
| .GST | MapInfo Corporation | Developer Files | MapInfo Geoset File | MapInfo Professional | Pitney Bowes |
| .GWD | Samsung Electronics | Developer Files | Gear Watchface Design File | Samsung Gear Watch Designer | Samsung Electronics |
| .GWF | Benthic Software | Developer Files | Benthic Golden Data File | Benthic Golden | Benthic Software |
| .GXP | Google | Developer Files | Google XML Pages Data | Google XML Pages | Google |
| .GXR | ARTech | Developer Files | GeneXus Report | GeneXus | ARTech |
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