Google has just released a tool called Swiffy which takes a Swf file and converts it to HTML5 - hence the name. Although still experimental it opens up lots of possibilities.
All you have to do to use Swiffy is provide the .swf file and it outputs HTML5 with the animation data coded using JSON.
The actual graphics are rendered using SVG and the level of SVG support has to be good. No prizes for guessing which browser has just this level of SVG support - Chrome, of course, but it also should work with Safari.
At the moment Swiffy is provided as a web service. You go to the web page, upload your file and it gets converted. Currently you can't get the source and Google hasn't decided if Swiffy is going to be open source or not.
Google says that such an early version can't be expected to convert all Flash content but it should work with timeline animations, vector graphics etc. A full Flash game is beyond it at the moment but you can see some examples of what it can do at a gallery site that Google has set up.
So far Swiffy isn't supposed to provide a solid alternative to Flash, just an experimental tool, but clearly it could be used as a way of getting Flash-based content onto Flash-hating Apple systems. It seems likely that this isn't the last we will hear of Swiffy.
Gallery of SWF files