Much more robust IDE than Adobe Flash Professional.

FlashDevelop is a must-have for anyone developing Flash and Adobe AIR software. Code completion speed by far is the fastest I've ever seen in any IDE for any language. Pressing a key pops up the code completion panel instantaneously, and it has never showed a degradation in performance even in projects with hundreds of source files, some of which being tens of thousands of lines long in some cases. Not to mention the debugger is a godsend. It is also by far the best windows IDE for developing with OpenFL and Haxe. It gets all the same benefits of AS3 code intelligence for the Haxe language.

Bandwidth efficient for multimedia content.