Dave Gnukem

Side scrolling shooter for Windows or Linux. (Open Source, GPL)
http://www.scorpioncity.com/djgame.html

Baroq

Arcade shooter for Windows with multiple power-ups that combine for more effective weapons.
http://www.sting.co.jp/play/baroshu/index2_e.htm

FireCrow

A shoot 'em up game for Windows. Includes information and downloads.
http://firecrow.ifrance.com/firecrow/

Electric Project Files

Windows shooter in which the goal is to hit the moving targets with your mouse. [Open Source]
http://planet-moritz.de/pfiles/game/pfilesgame.html

Space Plumber

First-person 3d game for Linux, not much different to Doom and Quake.
http://www.triptico.com/splumber/

A Tribute To Cactaur

2D shoot-them-up for Windows with a cactus that sprays tons of thorns.
http://spilocke.bravepages.com/

Corridors of Power

Describes first person shooter for Windows with textures, light maps, models, sound, and level editor.
http://www.apgsoftware.co.uk/cop/cop.html

Open Quartz

Describes 3D shooter based on the Quake engine, with source, maps, textures, and utlilities. (Open Source, GPL)
http://openquartz.sourceforge.net/

My Blitz Basic Programs

Source code available for Ms Blitzman, Scrabble, and Blitzum. Also has downloads for Deblitzer, Blitzatron, and MMMarbles.
http://www.incitti.com/Blitz/

Mortar Mayhem

A shooter for up to eight players for DOS or Windows.
http://jj.starthotel.dk/mortar/

HalfLight

Scrolling spaceship shooter for Windows. Game description and backstory, with links to reviews.
http://gapingwolf.com/halflight/

World War II Aces

2D aircraft shooter for Windows. Includes screen shots.
http://www.geocities.com/wwiiaces/

X-Bomber

2D 32-bit scrolling shooter for Windows, based on Japanese Science Fiction TV series "Star Fleet." News, screen shots, game background, and discussion forums.
http://www.xbomber.co.uk/

Meteor

Military shooter for DOS in which you control the main character in real-time.
http://www.jbgames.com/games/meteor/

Smashteroid

Clone of the Intellivision game Astrosmash for DOS or Windows in which you shoot aliens from the bottom of the screen. [Open Source]
http://www.ncdgames.com/games.php?game=smashteroid

EclipseGL

3D game in which 31 countries decide to reverse the information age by removing technology from all but a few vital sectors.
http://www.eclipsegl.com

Wulfram II

Online 3D shooter and strategy game allowing up to 64 players per server.
http://www.wulfram.com/

The Melody of Heaven Shooter Games

Includes two arcade-style clones: Cosmocrafter and Sea Sug Invasion.
http://www.freewebs.com/melodyofheaven/games.htm

Gaming's Evolution Team

Download free games and minigames.
http://www.freewebs.com/ge-team/

Protosphere

Includes news, screen shots, and downloads. Based on Quake II Engine source code.
http://www.yoshiware.com/index2.htm

Just Shoot the Thing

Shockwave shoot-em up for Windows featuring shields, bonus ships, powerups, 50 Sound effects, 10 built in targets, 3 different weapons and the ability to take any image from the clipboard and use it as the target.
http://www.digitalliquid.com/dldata/soft.html#just

D-Day Normandy

WWII shooter based on the Quake 2 engine. Offers downloads, screenshots and editing tools to download.
http://dynamic.gamespy.com/~ddc/site/

AQ2

Based on the Quake 2 engine. Offers screenshots, downloads, forums and progress reports.
http://www.cam-direct.co.uk/ltk/ltktbm.shtml