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

Scott's Space Invaders
They arrived one day. They attacked the outpost. Funny little green guys shooting purple energy zigzags. All would have been lost were it not for the lone defender in his little ship. He fought them. Wave after wave. They only kept coming faster and faster. ... Scott's Space Invaders is like the good ol' space invaders that you remember, but with a few additional perks and powerups, some new tricks, and designed to operate on modern PC hardware. ... Perhaps we'll never know... ... Did he ever defeat them all?
http://www.sb-software.com/spaceinvaders/sbvade16.exe - 3Mb - Download - Screenshot

Cash Invaders
Cash Invaders is a space shooting game for MS-DOS. You shoot aliens to earn money, with that money you can buy power-ups. There are 100 levels plus 9 bonus levels. The game mixes elements from Space Invaders, Blood Money, SpaceBastards and some other games. ... All graphics are raytraced with 3D Studio Max.
http://members.home.nl/bas.de.reuver/cashinvaders/invader.zip - 416Kb - 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

Jumpix
The XXII century. Our Earth is in danger. The invaders want to capture it and make their colony. For a long time the Earth was covered with a protective sphere. But the invaders have invented new weapons to destroy the protective sphere. The only chance to protect the Earth is to use a... You are given an opportunity to defeat of the invaders and get to the Space Intellect. ... Welcome to the board the space fighter and follow some instructions to control this machine. ... Each level makes you close to space Intellect.
http://www.gamexzone.com/files/jumpix.exe - 3Mb - Download - Screenshot

When Icons Attack
Your desktop icons are on a rampage. They have gone wild and are attempting to seize control of the desktop. Only one obstacle stands in there way -- you! This exciting space shooter features over 100 unique levels and rendered graphics. The game plays a bit like space invaders, with some galaga... The icons, of course, have been augmented with powerful weapons of their own, and it will be very challenging to defeat them all. ... Only you can stop the icon invaders. ... 0. ... Your actual desktop icons serve as the basis for the enemies that you will face.
http://www.sb-software.com/wheniconsattack/sbicon11.exe - 3Mb - 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

Dylo's Adventure - Windows
An old-school platform game where Dylo -a groovy dinosaur- gets involved in the adventure of ruining the twisted plans of the evil space invaders who want to conquer planet Earth and turn it into their own theme-park. Only armed with stones and boomerangs, Dylo shall do his best to give to those... Dylo will not only have to face the outer space menace, but the inhabitants and natural dangers of his homeworld as well. ... An interesting story with a touch of humor makes the game an amazing adventure.
http://www.southwindsgames.com/site/da/DylosAdventureSetup.exe - 6Mb - Download - Screenshot