One of the more challenging user experiences in a game is the need to move AND aim a player on the screen. That gets harder with mobile devices, where you have limited controller options. One way to fix this, is to allow the user to tap where your character should aim than have him turn in that direction. Think of a gun turret or a spaceship where all you do is tap on enemies and the turret or spaceship turns and fires in that direction.
Last year, I wrote a blog about creating your own simple collision detection code. I implemented this for a children's math game I created. You can refer to my blog here:
In the last few days, I have been working on a VT100 terminal entirely built within a web page. I use the HTML5 Canvas feature to draw the terminal surface and AJAX to a dedicated C# built server for the data flow. Well, I had this small annoying problem that the Canvas feature is not supported in Internet Explorer 6, 7 or 8. Since a lot of users use IE, it's an annoyance I wanted to try to fix.