Flixel is a free Actionscript library that enables ActionScript3 programmers to prototype and create new games quickly and easily. It's a pretty awesome tool, and games like Canabalt, Fathom and Tuper Tario Bros. (among many others!) wouldn't be around without it. So far, it's only been capable of developing Flash games for the PC/Mac, but pretty soon, we'll be able to make iPhone games with it.
During today's Canabalt postmortem (a summary of which is coming soon!), Adam "Atomic" Saltsman made this special announcement and went into a little more detail on what Flixel for iPhone will be capable of. In addition to its normal functionality, it will feature a rudimentary Actionscript 3-to-Objective-C translator to accelerate iPhone ports of Flixel games. There's still a lot for me to learn about programming, but I got a feeling having this development kit/framework at our disposal will make development for the platform a lot more accessible.
Flixel for iPhone is not yet finished, but a private release beta will begin very soon, with the public release to follow.