Often the OpenFL forum is better for such questions, assuming you intend to use OpenFL. I myself was searching for Spritesheet libraries there just yesterday.
Make sure you are first learning how to use OpenFL. You may not need an atlas/tilemap library if you do not have many graphics to display. You can go pretty far with the OpenFL Sprite class for example in many cases. You can also convert swf files and use them directly for some purposes.
There are built-in libraries in OpenFL: Tileset and Tilemap. If you run
openfl create bunnymark from the command line it gives an example of how to use those.
Some other tools/texture packers for SpriteSheets include TexturePacker, Shoebox, Zoé, and Others. Also HaxeFlixel Game Engine and Flump/Flambe/2dKit. Also GAF. The best tool depends on your desired workflow and end product of course. Any questions?