Looking for isometric game engines, I found three great projects: FFilmation, As3isolib and OpenSpace.

FFilmation (MIT License):

• Have a programming interface as small and easy as possible, no matter how complex the internal code is;
• Rendering performance is a major concern when designing all the algorythms;
• Graphic designers are able to work on the application’s ( game or not ) environments without any programming skills, visually, and with almost immediate previews of what they are doing.

As3isolib (MIT License):

• Simple scene creation;
• 3 primitive types;
• Base class for displaying user-created conten;
• Plenty of styling option on vector based primitive;
• Integrates well with a variety of tween engine;
• Improved 3D isometric positional sortin;
• Scene & view renderer classes geared towards performance optimizatio;
• Performance caching of static and animated sprite asset.

OpenSpace (commercial, part of the SmartFoxServer platform for multiplayer games):

• Engine and framework for rapid development of multi-user virtual worlds and MMO communities;
• Customizable tiles' aspect ratio;
• Tiles Elevation
• 2D objects in a 2.5D world
• Backgrounds and foregrounds
• Scrolling
• Advanced pathfinding
• Powerful avatar management
• Advanced map interaction system
• Exhaustive documentation
• Complete Map Editor

If you were planning to develop an isometric game, you just found your first step.

QuickBox2D is one of them. It is a mini-library created to work with Box2DFlashAS3, which is an AS3 port of the famous Box2D C++ physics engine. The main purpose of this library is to significantly simplify instantiation of rigid bodies and provide a simple way to bind them with custom graphics.

You can start with QuickBox2D by reading this great kick off tutorial. It explains the engine itself and demonstrate how to use some of it's features.

Sometimes the project has it´s own specific features and it requires a completly customized code, but most of the time it´s all about the same things: test input, check collisions, update a bunch of elements and finally render them all. Looking for a tool to do those tasks for me, I found two free and open source game engines: PushButton and Flixel.

PushButton is a very modular game engine licensed under the MIT license. It has core functionality as resource manager, logger, debug monitoring, serialization, time management, globally named objects, etc. It also has a set of components that make the engine even better:

• Physics based on Box2D;
• Gameplay components: health, teams, state machines;
• Sprite-based and SWF-based 2D rendering;
• Tilemap system;
• Pathfinding library;
• Basic networking. Pass events to/from your servers, do XMLRPC/JSON Web API requests, etc;
• Awesome UI capabilities via Flash - localizable, stylable/themable, internationalizable.

Flixel is collection of AS3 files that helps organize, automate, and optimize Flash games. It is also licensed under the MIT license and has a great set of features:

• Really fast renderer (5000+ sprites on modern PCs);
• Tilemaps;
• Particle systems;
• Global sound system with volume hotkeys, looping, panning, etc;
• Parallax scrolling (free/multi-directional);
• Built-in 2D box-based game physics (not Box2D);
• Fast text rendering;
• Retro style zoomed rendering options (2x pixels, 3x pixels, etc);
• Works great with non-pixel art too, with support for rotation, scaling;
• Composite multiple sprites using blending modes to create sweet lighting effects;
• Does not require the Flash IDE, works best with free tools like FlashDevelop;
• Organizational classes like game states;
• Simple buttons;
• Utilities for looping music and playing sound FX;
• Simple special effects like screen flashes and fades;
• Save game data between sessions using a local shared object.

Reading about them gave me the idea of writing my own game engine someday. Maybe some raining day I give it a try