sfxr is a generator for simple sound effects, created by DrPetter (http://www.drpetter.se). You can use it to create easy retro sounds for remixing or video games.
Increpare has created bfxr, a web remake of sfxr with many more exciting features: http://www.bfxr.net/
Thomas Vian from superflashbros.net ported sfxr to ActionScript 3. You can find it here: http://code.google.com/p/as3sfxr/ or you can get it like this: svn checkout http://sfxr.googlecode.com/svn/branches/as3sfxr as3sfxr
Chris Gassib has ported sfxr to the iPhone. You should be able to find it in the App Store. The code has been added as a branch that you can access like so: svn checkout http://sfxr.googlecode.com/svn/branches/sfxr-iPhoneOS sfxr-iPhoneOS