| gcd | Garmin Nuvi Software Update |
| gcd | General CADD Drawing |
| gcd | Mercury Refcode List Data |
| gcd | Microsoft SharePoint WorkSpace Groove Component Download |
| gcf | GameExchange2 Camera Data |
| gcg | GCG DNA Sequence |
| gci | Gamecube Game Save |
| gck | Gene Construction Kit Data |
| gcm | Gamecube Disk Image |
| gcn | RSView Machine Edition Global Connections Data |
| gco | G-code Code |
| gcod | G-code Code |
| gcode | G-code Code |
| gcp | Spectramap Group Properties |
| gcrd | GnomeCard vCard Data |
| gcs | Gamecube SharkSave Format Data |
| gcs | GameShark SharkSave Data |
| gct | GenePattern Gene Cluster Text |
| gctl | SCCM GIAM Control Data |
| gcw | Microsoft Mathematics Worksheet |
| gcz | Dolphin Emulator Archive |
| gd | STK Database Update Information |
| gd1 | Gerber Drill Drawing Data |
| gd2 | Gerber Drill Drawing Data |
| gd3 | Gerber Drill Drawing Data |
| gd3 | GreatFamily Genealogy Data |
| gd3 | SNES ROM Image GD3 |
| gdb | Act! Group Database |
| gdb | Genbox Family History Database |
| gdb | GroupMail Database |
| gdb | TIGER Geodatabase |
| gdc | FME Desktop Grid Data Catalog |
| gdd | Gerber Drill Drawing Data |
| gde | GDE Data |
| gde | GlobalQSL Graphic Editor Data |
