Flash files adds a great interactivity to web pages and applications. Still there are some devices like iPhones and iPads which doesn't support Flash embedded contents. However, with rapidly growing use of HTML5, Flash contents are no more used with them. As you know the advance version of this markup Language is capable of showing Flash-like content without any third party plug-in.
Google Swiffy is a free tool which converts SWF files (the file format for Flash) to HTML5 content. It uses SVG, a standardised format for vector graphics which is supported by most of latest web browsers. It supports shapes, embedded fonts, timeline animation, (dynamic) text, movie clips, buttons and scripting using Action Script 2.
The conversion can be done online and offline. To convert a file online, go to Google Swiffy home page and upload your SWF file. The converted file will then be available for downloading. You can see a preview also in mobile devices to test all the functionality of converted file. But be sure to download the output file within 15 minutes, after which the link will expire.
For offline and desktop conversion, you may have the Swiffy Extension, and directly publish to HTML5 from Adobe Flash Professional. After installing the extension, you may directly go to Commands->Export to HTML5 (Swiffy) menu to export the flash file to HTML5. Upon clicking, it will open the result file in the default web browser.
There is a similar tool available from Adobe, called Wallaby. However there is a major difference between these two extensions. Swiffy requires a SWF file for conversion while Wallaby needs a FLA file for conversion. Wallaby doesn't offer online conversion of files.