An open source shoot-em-up engine
This is a lovely work-in-progress shoot-em-up. It features procedural background terrain and rich enemy shooting patterns already. The code is open source, as are the graphics, so you're free to fork and adapt it.
Play the Game or Download the Source
is a proud sponsor of Phaser. As well as offering thousands of fun games to play, they also have a great revenue-sharing scheme
for developers who implement their ads.