Alien Outbreak
Are you ready for some serious action? AlienOutbreak is the most addictive space shooter in the entire solar system. And very well may be in all other galaxies as well (we? ll find out as soon as we make the first real contact with the aliens). The game sucks in immediately and does not let go... There are four episodes (each for a separate alien race you oppose), 201 unique levels, 40 different enemy units, plus 9 alien bosses. ... Show that alien scum what you are worth! ... shooters. ... kill them all?
http://www.beegames.com/alienoutbreak.exe - 3Mb - Download - Screenshot

Alien Stars
Welcome to the fantastic world of Alien Stars - a breathtaking vertical scrolling space shooter game! The game of our future. Leave your fears behind. Set your mind free. Believe in the endless universe and the millions of alien galaxies.
http://www.awem.com/download/AlienStarsSetup.exe - 11Mb - 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

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

Alien Flux
Defend Fluffies from invading aliens. Evil aliens attempt to mutate your Fluffies into malevolent Lime Jellies. You must defend them with your lasers, smartbombs, and missiles. Hardcore laser blasting arcade action similar to Williams' Defender. * Four huge fiendish bosses * Powerups galore * A... * Reaches the parts that other shooters cannot reach!!
http://www.puppygames.net/downloads/SetupAlienFluxDemo.exe - 10Mb - 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. ... With superior firepower and enhanced spaceship capabilities that can be upgraded from time to time and ability to build structures on your homeplanet to aid in overall defence you can turn your alien shooting into pure unrefined fun.
http://www.enkord.com/download/clash_n_slash_111.exe - 5Mb - Download - Screenshot

phoenicas
After a successful alien attack on earth, only 6 humans escaped. Five are onboard non-firing space vessels and one (you) is piloting the only remaining fighting craft. Your mission is to guard the vessels on the journey to safety. Aliens will attack the convoy and try to kill you and abduct the... Phoenicas is an arcade musical 2d shooter in the styles of defender, exerion, phoenix, ikaruga and space invaders. ... Phoenicas is an old school score-driven 2d shooter. ... It is a hardcore shooter at heart but has been made easier and more accessible for novices to enjoy also.
http://www.phoenicas.com/phoenicas/phoenicas_demo.exe - 16Mb - Download - Screenshot

Xeno Assault II
Blast aliens and save the universe in an all new sequel to one of the most highly praised games of this year. Xeno Assault II will capture your mind with breath taking game play and heart pounding arcade action the likes of which is rarely seen in a galaga based shooter. ... You will need speed, skill, cunning and a shear lust for destruction if you want to survive the thousands of alien craft that await you. ... But don't get too happy, you have 10 HUGE alien boss ships to fight, and believe me, their firepower will always be heavier than yours!
http://www.jaggedbladesoft.com/xenoassault2/Xeno2Demo.exe - 7Mb - Download - Screenshot

Acamar Rising
Acamar Rising is a 3D space shooter where a lone fighter must defend a space station against the many threats of space, from asteroids to aliens. The fighter pilot who defends the station may be lone, but he isn? t without some hefty resources at his disposal. ... Also alien crafts will continuously assault and harass the defenses, along with the occasional mother ship. ... Let too many of these items past and there won? ... t be anywhere to left to dock! ... With four power-ups to be found in asteroids and 8 different weapons to purchase, the defending ship will go from bucket of bolts to...
http://www.beteogames.com/acamar/AcamarSetup.exe - 16Mb - Download - Screenshot

Gunstorm
Gunstorm is a single screen space shooter. Mouse or keyboard controlled, Gunstorm is a top down arcade game where the player must ascend through ever-changing levels of alien waves, meeting different guardians along the way. Several game types are available, including a superb Asteroids inspired... Fully 3D and using the Cornutopia Hector graphics engine, Gunstorm represents the most advanced game in a series of releated shooter titles stretching back to 1992. ... Different weapons and enemy combinations, and different level types and guardians have all been extensively adjusted to make...
http://www.cornutopia.co.uk/software/taskforcesetup.exe - 3Mb - Download - Screenshot