| .J2B | Epic Games | Fişiere de jocuri | Jazz Jackrabbit 2 Music Data | Jazz Jackrabbit 2 | Epic Games |
| .J2D | Epic Games | Fişiere de jocuri | Jazz Jackrabbit Data File | Jazz Jackrabbit | Epic Games |
| .J2E | Epic Games | Fişiere de jocuri | Jazz Jackrabbit 2 Episode File | Jazz Jackrabbit 2 | Epic Games |
| .J2H | Epic Games | Fişiere de jocuri | Jazz Jackrabbit 2 High Scores | Jazz Jackrabbit 2 | Epic Games |
| .J2I | Epic Games | Fişiere de jocuri | Jazz Jackrabbit 2 Internet Server Link File | Jazz Jackrabbit 2 | Epic Games |
| .J2L | Epic Games | Fişiere de jocuri | Jazz Jackrabbit 2 Level File | Jazz Jackrabbit 2 | Epic Games |
| .J2T | Epic Games | Fişiere de jocuri | Jazz Jackrabbit 2 Tile Set | Jazz Jackrabbit 2 | Epic Games |
| .JA | Trainz portal | Fişiere de jocuri | Jet Archive | N3V Games Trainz Simulator | Trainz portal |
| .JAG | Jagex | Fişiere de jocuri | Jagex Data File | RuneScape | Jagex |
| .JAM | Sierra Entertainment | Fişiere de jocuri | Leisure Suit Larry Magna Cum Laude Archive File | Leisure Suit Larry: Magna Cum Laude | Sierra Entertainment |
| .JAP | Alexander S. Meshcheryakov | Fişiere de jocuri | Nonogram Puzzle File | QNonograms | Alexander S. Meshcheryakov |
| .JBL | id Software | Fişiere de jocuri | Doom Scene Add-on File | Doom | id Software |
| .JDF | Adobe Systems Incorporated | Fişiere de jocuri | Adobe Acrobat Job Definition File | Adobe Acrobat DC | Adobe Systems Incorporated |
| .JG6 | Lena Games | Fişiere de jocuri | BigJig Jigsaw Data | BigJig | Lena Games |
| .JIG | GameHouse | Fişiere de jocuri | GameHouse Puzzle Jigsaw Game Data | Jigsaw World | Inertia Software |
| .JIGSAW | Carolina Road Software L.L.C. | Fişiere de jocuri | Jigsaw Explorer Puzzle | Jigsaw Explorer | Carolina Road Software L.L.C. |
| .JKL | LucasArts Entertainment Company, LLC | Fişiere de jocuri | Jedi Knight File | Star Wars Jedi Knight: Dark Forces II | LucasArts Entertainment Company, LLC |
| .JKS | Oracle Corporation | Fişiere de jocuri | Java Keystore File | Unity Technologies Unity | Unity Technologies |
| .JMF | Chain Studios | Fişiere de jocuri | Jackhammer Project | J.A.C.K | Chain Studios |
| .JN1 | Epic Games | Fişiere de jocuri | Jill Of The Jungle Data File | Jill Of The Jungle | Epic Games |
| .JNC | Hypnos Entertainment | Fişiere de jocuri | Jack Nicklaus 6 Course Data | Jack Nicklaus 6: Golden Bear Challenge | Hypnos Entertainment |
| .JNK | Little Green Men Games | Fişiere de jocuri | Starpoint Gemini 2 Junkyard Data | Starpoint Gemini 2 | Little Green Men Games |
| .JPK | JPK Instruments | Fişiere de jocuri | JPK Instruments File Format | Unknown Software | Unknown Developer |
| .JPN | Microsoft Corporation | Fişiere de jocuri | Windows Japanese Noise-Word List File | Microsoft Notepad | Microsoft Corporation |
| .JPP | Bitz & Pixelz | Fişiere de jocuri | Jigsaw Puzzle Player Puzzle Definition | Jigsaw Puzzle Player | Bitz & Pixelz |
| .JPZ | WordWeb Software | Fişiere de jocuri | Puzzle Solver Puzzle File | Crossword Solver | WordWeb Software |
| .JRC | Open Source | Fişiere de jocuri | PCjr Cartridge ROM File | DOSBox | Open Source |
| .JRF | Unknown Developer | Fişiere de jocuri | The Jumbot Bot Level Navigation Data | Half-Life | Valve |
| .JRL | BioWare | Fişiere de jocuri | BioWare Aurora Game Engine Journal Data | BioWare Neverwinter Nights | BioWare |
| .JST | Jabosoft | Fişiere de jocuri | Jnes Save State | Jnes | Jabosoft |
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