Space Alien Invaders
Free arcade style space shooter game for the PC.
http://www.freewareshareware.net/download/sai.exe - 1Mb - Download - Screenshot

Invasion 3D
Invasion 3D is a free multi-platform 3D arcade game, based on OpenGL and SDL and available for Windows and Linux. This fun and addictive game features realistic physics simulation, challenging gameplay, stunning visual effects,multiple weapons, hidden bonuses, and more. ... Invasion 3D was Inspired by Taito's original Space Invaders arcade game from 1978, and is dedicated to the MAME arcade emulator system. ... Create massive destruction and rack up as many points as you can as you blast your way through 20 waves with thousands of aggressive space invaders!
http://www.fascinationsoftware.com/FS/media/Invasion3D.tar.gz - 2Mb - Download - Screenshot

Typing Invaders - Free Typing Game
Typing Invaders is a REAL arcade game, in which you are escaping from invaders, shooting and trying to hit invaders. This is no fake - you are playing space invaders ! (You are not just typing characters). With this free typing game you WILL have fun, but don't worry, by playing Typing Invaders... Improve your typing skills with this free typing tutor - typing game !
http://www.giletech.net/Typing-Tutor/TInv_Setup.exe - 1Mb - Download - Screenshot

Alien Invaders Attack!
Free arcade style space shooter game for the PC.
http://www.sci-fi-game.com/download/aia.exe - 4Mb - Download - Screenshot

Star Reaver
Star Reaver is a freeware arcade style space shooter game, available for free download. Defend your ship from dive bombing alien space invaders. Grab the power ups for powerful new multi-directional weapons that shred the marauding invaders. Free download available for PC and Mac.
http://www.freewareshareware.net/download/sr.exe - 2Mb - Download - Screenshot

Da Browser Based Games Browser
Da Browser Based Games Browser is a custom games web browser that delivers easy navigation to arcade classics (Pac Man, Tetris, Asteroids, Space Invaders, etc), browser based games, browser based game websites, and web game directories. The distinctive feature of Da Browser Based Games Browser... Da Browser Based Games Browser will simply provide easy access to thousands of web games to the web games enthusiast. ... In addition, Da Browser Based Games Browser is equipped with an integrated search engine utilizing the popular search engines and allows you to save and access your favorite...
http://www.4comtech.com/vb/gamesbrowsersetup.exe - 2Mb - Download - Screenshot

Clash N Slash
Enjoy non-stop action space shooter with extremely simple controls suitable for all ages! Clash'N Slash, a totally new and highly addictive arcade space shooter for players who want to enjoy a fresh exciting gameplay and bored with playing tons of indistinguishable shooter games. ... In Clash'N Slash arcade game you must defend your planet from pesky alien invaders that will arrive from all around the galaxy. ... Loads of weapons, upgrades, enemies will hold you for a long time and innovative bonus triggering system will make your game experience colorful and fun.
http://www.enkord.com/download/clash_n_slash_111.exe - 5Mb - Download - Screenshot

Star Defender II
Star Defender II is a Space Shooter Arcade. It is developed like an advanced clone of old classic Galaga and possesses all the best features of this genre. Again in this fabulous Shoot'em up game you will get a chance to destroy enormous armies of the cruel invaders and to save the Galaxy! ... Every new mission has different background witch puts you into the atmosphere of the real Space Battle. ... Your small but manoeuvrable space ship is controlled by your mouse. ... The game includes seven missions with a wicked and mighty Boss at the end of each of them.
http://www.awem.com/download/StarDefender2Setup.exe - 8Mb - Download - Screenshot

Robot Invasion
Blow away ruthless robot invaders by the hundreds in this fast paced 3rd person 3D shooter. You'll be battling robots in diverse and awesome environments, while trying to save as many humans as possible. Some of the places you'll do battle are a spooky castle, ghastly grave yard, a space station... Pure adredaline filled action awaits anyone who takes on the mission to save humanity in this fast paced action arcade game. ... You'll battle a large variety of robots that become ever more ruthless as you progress through the game.
http://www.best3dgames.net/roboinv/roboinvd.zip - 13Mb - Download - Screenshot

Astro Hunter 3D Deluxe
One man... One ship... One infinite supply of Mark-1 nuclear torpedoes. They called him the astro hunter, and his job was to keep the shipping lanes clear. The UFOs tried to stop him -- they failed. Some say he even defeated the space invaders. This is his story, and it's a story you know well,... Astro Hunter 3D Deluxe is an asteroid shooter arcade game for your windows XP computer. ... It all started one day, when you downloaded what you thought was a simple "game" from the internet... ... It uses 3D graphics, and requires microsoft directx 9.
http://www.sb-software.com/astrohunter/sbastr18.exe - 3Mb - Download - Screenshot