GPL licensed (39)

Hexen: Beyond Heretic

Also known as Heretic 2

Adventure, 1995
Playable demo, Preview, FAQ

Kaos

First-Person Shooter, 2003
Freeware (installed), Freeware

Linley's Dungeon Crawl

Role-Playing, 1997
Freeware (installed), Freeware, Source code, Freeware

Mirror Magic

Puzzle, 2001
Freeware, Freeware, Freeware

MULE

Turn-Based Strategy, 1999
Freeware (installed), Freeware, Source code

NetHack

Role-Playing, 1987
Freeware, System component, Source code

NetHack Plus

Role-Playing, 1994
Freeware

NetHack: Falcon's Eye

Role-Playing, 2000
Freeware, Freeware, Source code

NGE Nibbles

Arcade, 2003
Freeware (installed), Freeware, Source code

Open Quartz

First-Person Shooter, 2004
Freeware, Update

Ptakovina

Puzzle, 2017
Freeware, Source code

Rise of the Triad

Also known as ROTT, Rise of the Triad: The HUNT Begins, Rise of the Triad: Dark War

First-Person Shooter, 1994
Shareware (installed), Shareware, Game expansion, Extra, FAQ

Robot Redemption

First-Person Shooter, 2014
Freeware

Rocks 'N' Diamonds

Puzzle, 1998
Freeware

Scavenger

Platform, 1996
Full version (installed), Full version

Ski Jump International v3

Also known as SJ3

Sport, 2000
Full version