| gcg | GCG DNA Sequence |
| gci | Gamecube Game Save |
| gcm | Gamecube Disk Image |
| gco | G-code Code |
| gcod | G-code Code |
| gcode | G-code Code |
| gcp | Spectramap Group Properties |
| gcrd | GnomeCard vCard Data |
| gct | GenePattern Gene Cluster Text |
| gctl | SCCM GIAM Control Data |
| gcw | Microsoft Mathematics Worksheet |
| gd | STK Database Update Information |
| gd1 | Gerber Drill Drawing Data |
| gd2 | Gerber Drill Drawing Data |
| gd3 | Gerber Drill Drawing Data |
| gd3 | SNES ROM Image GD3 |
| gdb | TIGER Geodatabase |
| gdb | Genbox Family History Database |
| gdd | Gerber Drill Drawing Data |
| gdi | Sega Dreamcast GDI Image |
| gdiagramstyle | OmniGraffle Diagram Style |
| gdo | Gerber Data Object |
| gdq | SmartWare Quick Graph |
| gdsp | Astound GDSP Data |
| gdt | Guitar and Drum Trainer Song |
| gdx | Novapoint Triangle Model |
| gdx | GAMS Data Exchange File |
| gdy | Novapoint Triangle Model |
| gdyn | Gimp Dynamics File |
| ge3 | Mastercam Geometry Data |
| ge6 | WinFamily 6 Genealogy Data |
| geb | Sybase PowerDesigner Glossary Model Backup |
| geb | Dr. Hardware Data File |
| gedata | Qlucore Omics Explorer Data File |
| gee | GeeonxCreator Object Data |