Octobinz from developperstune, shares his R-Type clone on Nintendo DS using PALib and has made the source code available to us.

An R-Type is a horizontally-scrolling shoot-em-up arcade game produced by Irem in 1987. You are on board a futuristic fighter craft called R-9a Arrowhead, your mission is to blast off and strike the evil Bydo Empire into pieces.

So if you're up for some intergalactic, out of this world, Top Gun fun, then get your hands on these R-Type goodies.