Quote: "I ask if exist a level design software for AppGameKit ?"
The answer, of course, is YES. There are lots of level editors you could use to create a level for an AppGameKit game, but you'll need to write the software (in AGK) to load the level. AppGameKit is a language, not a game engine. If you want 2D Physics in your game, then you might use something like
RUBE for building the 3d layout of your level. There's even a RUBE loader for AppGameKit somewhere.
If you take a look over on the showcase board, Baxslash is creating a
fantastic level editor, that also exports the AppGameKit code required to load the level - WIN!
A "level" can mean lots of things, so finding the right tools for the job really depends on the type of game you want to create. Many developers will write their own level editor to suit the specific type of game they are creating (for example, I wrote an editor for a bike game (that never got finished) example vid can be seen here:
https://forum.thegamecreators.com/thread/212158#msg2536599