I made this a couple of months ago but didn't release it because I was planning on adding some more features (bunkers and high scores) and gave up on it. Now that I've completely given up on it and moved on to other things, I've decided to release it without those features.
Other than having no bunkers, its graphics and gameplay are almost exactly the same as the original Space Invaders.
The download, screenshot, and source code can be found here:
http://viewsourcecode.org/homebrew/space-invaders