Native support for Adobe® AIR™ – Flex Builder 3 adds support for Adobe AIR which lets developers use their existing web development skills in HTML, AJAX, Flash, and Flex to build and deploy RIAs to the desktop.
Adobe AIR features include AIR project creation and Export Release Build in AIR format.
The Flex Builder 3 download page lets you download a trial version.
For instructions on installing just Flex 3 SDK, see Flex 3 SDK Installation Instructions.
Note: This post assumes you followed installing Apache, PHP, and My SQL on Mac OS X El Capitan and have since upgraded to Mac OS X Sierra.